Apply upstream performance improvement to _get_block_templates_paths

[WunderBart]

Original request: pcShBQ-1x1-p2

_get_block_templates_paths had recently received a performance bump. We can't use it directly since it's marked as @access private, but we can surely apply those improvements to our implementation, e.g.,

woocommerce/plugins/woocommerce/src/Blocks/Utils/BlockTemplateUtils.php

Lines 270 to 280 in 2f88da5

	public static function get_template_paths( $base_directory ) {
	$path_list = array();
	if ( file_exists( $base_directory ) ) {
	$nested_files = new \RecursiveIteratorIterator( new \RecursiveDirectoryIterator( $base_directory ) );
	$nested_html_files = new \RegexIterator( $nested_files, '/^.+\.html$/i', \RecursiveRegexIterator::GET_MATCH );
	foreach ( $nested_html_files as $path => $file ) {
	$path_list[] = $path;
	}
	}
	return $path_list;
	}

cc: @joshuatf @tjcafferkey @gigitux