Media: Update post mime type when image format is converted during upload.

When uploading HEIC files via the media library on servers that support
HEIC, the image is correctly converted to JPEG on disk but the
attachment post's `post_mime_type` remained `image/heic`. This updates
`_wp_image_meta_replace_original()` to also update the post mime type
when the saved image format differs from the original.

Additionally fixes the REST API index to use `wp_get_image_editor_output_format()`
so the `image_output_formats` response includes the default HEIC-to-JPEG
mapping, enabling client-side media processing to be aware of it.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: adamsilverstein

src/wp-admin/includes/image.php

@@ -209,6 +209,20 @@ function _wp_image_meta_replace_original( $saved_data, $original_file, $image_me
 	// Update the attached file meta.
 	update_attached_file( $attachment_id, $new_file );
 
+	// Update the post mime type if the image was converted to a different format.
+	if ( ! empty( $saved_data['mime-type'] ) ) {
+		$post = get_post( $attachment_id );
+
+		if ( $post && $post->post_mime_type !== $saved_data['mime-type'] ) {
+			wp_update_post(
+				array(
+					'ID'             => $attachment_id,
+					'post_mime_type' => $saved_data['mime-type'],
+				)
+			);
+		}
+	}
+
 	// Width and height of the new image.
 	$image_meta['width']  = $saved_data['width'];
 	$image_meta['height'] = $saved_data['height'];

src/wp-includes/rest-api/class-wp-rest-server.php

@@ -1383,8 +1383,10 @@ public function get_index( $request ) {
 			$input_formats  = array( 'image/jpeg', 'image/png', 'image/gif', 'image/webp', 'image/avif', 'image/heic' );
 			$output_formats = array();
 			foreach ( $input_formats as $mime_type ) {
-				/** This filter is documented in wp-includes/media.php */
-				$output_formats = apply_filters( 'image_editor_output_format', $output_formats, '', $mime_type );
+				$output_format = wp_get_image_editor_output_format( '', $mime_type );
+				if ( ! empty( $output_format[ $mime_type ] ) && $output_format[ $mime_type ] !== $mime_type ) {
+					$output_formats[ $mime_type ] = $output_format[ $mime_type ];
+				}
 			}
 			$available['image_output_formats'] = (object) $output_formats;