Optimize Less_Visitor::visitObj for performance

All this small piece of code does are a few string manipulations.
It's not very expensive. But called a lot. More than 800,000 times
just when running the tests in this codebase. This adds up.

Caching the strings in a map reduces the number of calls to how many
classes actually exist: only 35.

This is well visible in a profile. The relative "self" time spend in
this method goes down from 13 to 8. The relative total time for this
method goes down as well, from about 190 to 160.

Bug: T381895
Change-Id: I10e0c23f72dc5f4babb38f3059716945f5177a4c

lib/Less/Visitor.php

@@ -13,6 +13,8 @@ public function __construct() {
 	}
 
 	public function visitObj( $node ) {
+		static $funcNames = [];
+
 		if ( !$node || !is_object( $node ) ) {
 			return $node;
 		}
@@ -27,9 +29,10 @@ public function visitObj( $node ) {
 		//
 		// https://packagist.org/packages/brianhenryie/strauss
 		// https://packagist.org/packages/coenjacobs/mozart
-		$nodeClassNameParts = explode( 'Less_Tree_', get_class( $node ), 2 );
-		$nodeType = end( $nodeClassNameParts );
-		$funcName = 'visit' . strtr( $nodeType, [ '_' => '', '\\' => '' ] );
+		$class = get_class( $node );
+		$funcName = $funcNames[$class] ??= 'visit' . str_replace( [ '_', '\\' ], '',
+			substr( $class, strpos( $class, 'Less_Tree_' ) + 10 )
+		);
 
 		if ( isset( $this->_visitFnCache[$funcName] ) ) {
 			$visitDeeper = true;