HTML API: Add missing insertion mode constants.

As the HTML Processor starts to support other insertion modes outside of
"IN BODY" it needs to be aware of those other modes. This patch
introduces the missing insertion modes in preparation for adding that
support.

Extracted as necessary prep work to the following more complete change:
#6020

Props jonsurrell.
See #61549.


git-svn-id: https://develop.svn.wordpress.org/trunk@58631 602fd350-edb4-49c9-b593-d223f7449a82

Author: dmsnell

src/wp-includes/html-api/class-wp-html-processor-state.php

@@ -59,6 +59,162 @@ class WP_HTML_Processor_State {
 	 */
 	const INSERTION_MODE_IN_BODY = 'insertion-mode-in-body';
 
+	/**
+	 * In select insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-inselect
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_SELECT = 'insertion-mode-in-select';
+
+	/**
+	 * In select in table insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-inselectintable
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_SELECT_IN_TABLE = 'insertion-mode-in-select-in-table';
+
+	/**
+	 * In table insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-intable
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_TABLE = 'insertion-mode-in-table';
+
+	/**
+	 * In caption insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-incaption
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_CAPTION = 'insertion-mode-in-caption';
+
+	/**
+	 * In table body insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-intablebody
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_TABLE_BODY = 'insertion-mode-in-table-body';
+
+	/**
+	 * In row insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-inrow
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_ROW = 'insertion-mode-in-row';
+
+	/**
+	 * In cell insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-incell
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_CELL = 'insertion-mode-in-cell';
+
+	/**
+	 * In column group insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-incolumngroup
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_COLUMN_GROUP = 'insertion-mode-in-column-group';
+
+	/**
+	 * In frameset insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-inframeset
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_FRAMESET = 'insertion-mode-in-frameset';
+
+	/**
+	 * In head insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-inhead
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_HEAD = 'insertion-mode-in-head';
+
+	/**
+	 * Before head insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-beforehead
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_BEFORE_HEAD = 'insertion-mode-before-head';
+
+	/**
+	 * After head insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-afterhead
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_AFTER_HEAD = 'insertion-mode-after-head';
+
+	/**
+	 * In template insertion mode for full HTML parser.
+	 *
+	 * @since 6.7.0
+	 *
+	 * @see https://html.spec.whatwg.org/#parsing-main-intemplate
+	 * @see WP_HTML_Processor_State::$insertion_mode
+	 *
+	 * @var string
+	 */
+	const INSERTION_MODE_IN_TEMPLATE = 'insertion-mode-in-template';
+
 	/**
 	 * Tracks open elements while scanning HTML.
 	 *