Themes: Add filter for excluding directories from being scanned for template files.

Exclude 'node_modules' directories from paths searched in `WP_Theme::scandir()`. Introduces the `theme_scandir_exclusions` filter to allow sites to exclude any other paths like `bower_components` or `vendor` from being searched for template files.

Props lukasbesch, dd32, swisspidy, rachelbaker. 
Fixes #38292. 

Built from https://develop.svn.wordpress.org/trunk@40301


git-svn-id: http://core.svn.wordpress.org/trunk@40208 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-theme.php

@@ -1155,11 +1155,21 @@ final class WP_Theme implements ArrayAccess {
 		$results = scandir( $path );
 		$files = array();
 
+		/**
+		 * Filters the array of excluded directories and files while scanning theme folder.
+		 *
+ 		 * @since 4.7.4
+		 *
+		 * @param array $exclusions Array of excluded directories and files.
+		 */
+		$exclusions = (array) apply_filters( 'theme_scandir_exclusions', array( 'CVS', 'node_modules' ) );
+
 		foreach ( $results as $result ) {
-			if ( '.' == $result[0] )
+			if ( '.' == $result[0] || in_array( $result, $exclusions, true ) ) {
 				continue;
+			}
 			if ( is_dir( $path . '/' . $result ) ) {
-				if ( ! $depth || 'CVS' == $result )
+				if ( ! $depth )
 					continue;
 				$found = self::scandir( $path . '/' . $result, $extensions, $depth - 1 , $relative_path . $result );
 				$files = array_merge_recursive( $files, $found );

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-40300';
+$wp_version = '4.8-alpha-40301';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.