Since RO_SPACE strings cannot be written to after creation, they cannot
be internalized later. This adds checks to normal string construction
methods that they are not created with TENURED_READ_ONLY.

Also changes the Symbol construction in setup-heap-internal.cc to use
internalized strings, which increases the number of internalized
RO_SPACE strings from 490 to 514 (915 including OLD_SPACE).

Bug: chromium:911416
Change-Id: I222ff883e98f3a2f4ce70d369f22273f5c9edb0b
Reviewed-on: https://chromium-review.googlesource.com/c/1365279Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58074}