LocaleBuilder validates better, it also fixes most cases in
transformed-ext-invalid except one.

Bug: v8:10447
Change-Id: I6fed6692ca3264198e42ccc3d9ca4bfb54fb0517
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2549688
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71300}