rid nearly all use of ExceptionRef in zig (#15100)

Co-authored-by: nektro <nektro@users.noreply.github.com>

src/string.zig

@@ -720,7 +720,7 @@ pub const String = extern struct {
         if (BunString__fromJS(globalObject, value, &out)) {
             return out;
         } else {
-            return null;
+            return null; //TODO: return error.JSError
         }
     }