Add lock to AlternativeStateNameMap.

To prevent the class from accessing its localized_state_names_map_ and
localized_state_names_reverse_lookup_map_ members, a lock is added. It
locks all reads/write from the aforementioned members.

Bug: 1360571, 1414241, 1425951
Change-Id: Ic01b0cba3878748617863274deb04ec9e13645d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4352658
Reviewed-by: Christoph Schwering <schwering@google.com>
Commit-Queue: Florian Leimgruber <fleimgruber@google.com>
Cr-Commit-Position: refs/heads/main@{#1119411}