This is a part of larger cl https://chromium-review.googlesource.com/c/v8/v8/+/1144524
"Port canonicalizeLanguageTag and isStructuallyValidLanguageTag from JS to C++."

This is being separated out because:
1) this will unblock ftang's work
2) there is an increased memory usage issue report I'd like to understand before
   connecting IsStructurallyValidLanguageTag for widespread usage

The memory concern will be dealt with in a follow-up cl.

Also in this cl:
Fix to ignore the first tag when checking for duplicate subtags.

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I76f4f6861490d8f9ccb36d6a0f7a7d5fa32ff995
Reviewed-on: https://chromium-review.googlesource.com/1147561Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Jungshik Shin <jshin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Brian Stell <bstell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54653}