Docs: Add a comment about the $title global usage in various admin files.

This should make it clear that the variable is used as part of the HTML `<title>` tag on admin screens.

Props ravipatel, hellofromTonya, sabernhardt, audrasjb, SergeyBiryukov.
Fixes #53729.

git-svn-id: https://develop.svn.wordpress.org/trunk@51475 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/user-edit.php

@@ -32,8 +32,10 @@ if ( wp_is_application_passwords_available_for_user( $user_id ) ) {
 }
 
 if ( IS_PROFILE_PAGE ) {
+	// Used in the HTML title tag.
 	$title = __( 'Profile' );
 } else {
+	// Used in the HTML title tag.
 	/* translators: %s: User's display name. */
 	$title = __( 'Edit User %s' );
 }