Media: Prevent uploading and show an error message when the server doesn't support editing of WebP images, take II. Add new, better error message for it.

Props antpb, joedolson, iandunn, azaozz.
Fixes #53475.

git-svn-id: https://develop.svn.wordpress.org/trunk@51227 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/media.php

@@ -3858,6 +3858,11 @@ function wp_plupload_default_settings() {
 		$defaults['multi_selection'] = false;
 	}
 
+	// Check if WebP images can be edited.
+	if ( ! wp_image_editor_supports( array( 'mime_type' => 'image/webp' ) ) ) {
+	    $defaults['webp_upload_error'] = true;
+	}
+
 	/**
 	 * Filters the Plupload default settings.
 	 *