Social: Prevent the editor extension loading for unsupported post types

There's a bug #20357 that means if code is loaded that relies on the
`@wordpress/editor` or `@wordpress/edit-post` packages, then it crashes
the Site Editor.

This change checks the post type being editted and whether it supports
Publicize. If it doesn't, we skip loading the JS code.

projects/plugins/social/changelog/fix-social-site-editor

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Site Editor: Prevent the editor extension loading for unsupported post types

projects/plugins/social/src/class-jetpack-social.php

@@ -161,11 +161,25 @@ public function initial_state() {
 		);
 	}
 
+	/**
+	 * Checks to see if the current post supports Publicize
+	 *
+	 * @return boolean True if Publicize is supported
+	 */
+	public function is_supported_post() {
+		$post_type = get_post_type();
+		return ! empty( $post_type ) && post_type_supports( $post_type, 'publicize' );
+	}
+
 	/**
 	 * Enqueue block editor scripts and styles.
 	 */
 	public function enqueue_block_editor_scripts() {
-		if ( ! ( new Modules() )->is_active( self::JETPACK_PUBLICIZE_MODULE_SLUG ) || class_exists( 'Jetpack' ) ) {
+		if (
+			! ( new Modules() )->is_active( self::JETPACK_PUBLICIZE_MODULE_SLUG ) ||
+			class_exists( 'Jetpack' ) ||
+			! $this->is_supported_post()
+		) {
 			return;
 		}