path: remove StringPrototypeCharCodeAt from posix.extname

PR-URL: #54546
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/path.js

@@ -1462,8 +1462,8 @@ const posix = {
     // after any path separator we find
     let preDotState = 0;
     for (let i = path.length - 1; i >= 0; --i) {
-      const code = StringPrototypeCharCodeAt(path, i);
-      if (code === CHAR_FORWARD_SLASH) {
+      const char = path[i];
+      if (char === '/') {
         // If we reached a path separator that was not part of a set of path
         // separators at the end of the string, stop now
         if (!matchedSlash) {
@@ -1478,7 +1478,7 @@ const posix = {
         matchedSlash = false;
         end = i + 1;
       }
-      if (code === CHAR_DOT) {
+      if (char === '.') {
         // If this is our first dot, mark it as the start of our extension
         if (startDot === -1)
           startDot = i;