Editor: Add excerpt support to the wp_block post type.

The purpose is to enable using the excerpt as a description for user-created patterns on the Site Editor Pattern screens.

This commit backports the original PR from Gutenberg repository:
* [[https://github.com/WordPress/gutenberg/pull/60549|#60549: [Data Views] User patterns: Use excerpt as description]]

Reference: [[https://github.com/WordPress/gutenberg/issues/55244|#55244: Patterns: Add descriptions to user-created patterns]].

Follow-up to [44146], [44150], [50835], [56030].

Props poena, ntsekouras, krupalpanchal.
Fixes #61250.

git-svn-id: https://develop.svn.wordpress.org/trunk@58184 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/post.php

@@ -328,6 +328,7 @@ function create_initial_post_types() {
 			'map_meta_cap'          => true,
 			'supports'              => array(
 				'title',
+				'excerpt',
 				'editor',
 				'revisions',
 				'custom-fields',

tests/qunit/fixtures/wp-api-generated.js

@@ -3879,6 +3879,40 @@ mockedApiResponse.Schema = {
                             },
                             "required": false
                         },
+                        "excerpt": {
+                            "description": "The excerpt for the post.",
+                            "type": "object",
+                            "properties": {
+                                "raw": {
+                                    "description": "Excerpt for the post, as it exists in the database.",
+                                    "type": "string",
+                                    "context": [
+                                        "edit"
+                                    ]
+                                },
+                                "rendered": {
+                                    "description": "HTML excerpt for the post, transformed for display.",
+                                    "type": "string",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                },
+                                "protected": {
+                                    "description": "Whether the excerpt is protected with a password.",
+                                    "type": "boolean",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                }
+                            },
+                            "required": false
+                        },
                         "meta": {
                             "description": "Meta fields.",
                             "type": "object",
@@ -3939,6 +3973,11 @@ mockedApiResponse.Schema = {
                             "default": "view",
                             "required": false
                         },
+                        "excerpt_length": {
+                            "description": "Override the default excerpt length.",
+                            "type": "integer",
+                            "required": false
+                        },
                         "password": {
                             "description": "The password for the post if it is password protected.",
                             "type": "string",
@@ -4049,6 +4088,40 @@ mockedApiResponse.Schema = {
                             },
                             "required": false
                         },
+                        "excerpt": {
+                            "description": "The excerpt for the post.",
+                            "type": "object",
+                            "properties": {
+                                "raw": {
+                                    "description": "Excerpt for the post, as it exists in the database.",
+                                    "type": "string",
+                                    "context": [
+                                        "edit"
+                                    ]
+                                },
+                                "rendered": {
+                                    "description": "HTML excerpt for the post, transformed for display.",
+                                    "type": "string",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                },
+                                "protected": {
+                                    "description": "Whether the excerpt is protected with a password.",
+                                    "type": "boolean",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                }
+                            },
+                            "required": false
+                        },
                         "meta": {
                             "description": "Meta fields.",
                             "type": "object",
@@ -4379,6 +4452,40 @@ mockedApiResponse.Schema = {
                             },
                             "required": false
                         },
+                        "excerpt": {
+                            "description": "The excerpt for the post.",
+                            "type": "object",
+                            "properties": {
+                                "raw": {
+                                    "description": "Excerpt for the post, as it exists in the database.",
+                                    "type": "string",
+                                    "context": [
+                                        "edit"
+                                    ]
+                                },
+                                "rendered": {
+                                    "description": "HTML excerpt for the post, transformed for display.",
+                                    "type": "string",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                },
+                                "protected": {
+                                    "description": "Whether the excerpt is protected with a password.",
+                                    "type": "boolean",
+                                    "context": [
+                                        "view",
+                                        "edit",
+                                        "embed"
+                                    ],
+                                    "readonly": true
+                                }
+                            },
+                            "required": false
+                        },
                         "meta": {
                             "description": "Meta fields.",
                             "type": "object",