Speed up token value to name lookup

Grammar test suite sped up from 1.2 seconds to 1.1 seconds.

This went from O(n) (loop over 183 constants) to O(1) (hash lookup)

Author: TysonAndre

src/Token.php

@@ -59,15 +59,25 @@ public function getEndPosition() {
         return $this->fullStart + $this->length;
     }
 
-    public static function getTokenKindNameFromValue($kindName) {
-        $constants = (new \ReflectionClass("Microsoft\\PhpParser\\TokenKind"))->getConstants();
-        foreach ($constants as $name => $val) {
-            if ($val == $kindName) {
-                $kindName = $name;
-                break;
-            }
+    /**
+     * @return string[] - A hash map of the format [int $tokenKind => string $tokenName]
+     */
+    private static function getTokenKindNameFromValueMap() {
+        static $mapToKindName;
+        if ($mapToKindName === null) {
+            $constants = (new \ReflectionClass("Microsoft\\PhpParser\\TokenKind"))->getConstants();
+            $mapToKindName = \array_flip($constants);
         }
-        return $kindName;
+        return $mapToKindName;
+    }
+
+    /**
+     * @param int $kind
+     * @return string (Or int, if the kind name for $kind wasn't found)
+     */
+    public static function getTokenKindNameFromValue($kind) {
+        $mapToKindName = self::getTokenKindNameFromValueMap();
+        return $mapToKindName[$kind] ?? $kind;
     }
 
     public function jsonSerialize() {