lib.isStringLike: Remove use of list

In the current implementation of Nix, this list would be allocated
over and over. Iirc pennae tried to optimize static list allocation,
but gained no significant performance improvement.

lib/strings.nix

@@ -18,6 +18,7 @@ rec {
     isInt
     isList
     isAttrs
+    isPath
     isString
     match
     parseDrvName
@@ -821,7 +822,8 @@ rec {
      string interpolations and in most functions that expect a string.
    */
   isStringLike = x:
-    elem (typeOf x) [ "path" "string" ] ||
+    isString x ||
+    isPath x ||
     x ? outPath ||
     x ? __toString;