path: improve normalization performance

PR-URL: #28948
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

lib/path.js

@@ -95,7 +95,10 @@ function normalizeString(path, allowAboveRoot, separator, isPathSeparator) {
           lastSegmentLength = 2;
         }
       } else {
-        res += (res.length > 0 ? separator : '') + path.slice(lastSlash + 1, i);
+        if (res.length > 0)
+          res += `${separator}${path.slice(lastSlash + 1, i)}`;
+        else
+          res = path.slice(lastSlash + 1, i);
         lastSegmentLength = i - lastSlash - 1;
       }
       lastSlash = i;