Editor: Ensure that the block editor can be used on the page post type.

Additionally, add a notice for when you are editing the "latest posts" page.

Fixes #45537.

Props cameronjonesweb, swissspidy, hannahmalcolm, Fantasy1125, ArnaudBan, grantmkin, youknowriad, knutsp, SergeyBiryukov, audrasjb, whyisjake. 


git-svn-id: https://develop.svn.wordpress.org/trunk@51116 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/template.php

@@ -2674,3 +2674,20 @@ function wp_star_rating( $args = array() ) {
 function _wp_posts_page_notice() {
 	echo '<div class="notice notice-warning inline"><p>' . __( 'You are currently editing the page that shows your latest posts.' ) . '</p></div>';
 }
+
+/**
+ * Output a notice when editing the page for posts in the block editor (internal use only).
+ *
+ * @ignore
+ * @since 5.8.0
+ */
+function _wp_block_editor_posts_page_notice() {
+	wp_add_inline_script(
+		'wp-notices',
+		sprintf(
+			'wp.data.dispatch( "core/notices" ).createWarningNotice( "%s", { isDismissible: false } )',
+			__( 'You are currently editing the page that shows your latest posts.' )
+		),
+		'after'
+	);
+}