Tests for raw_ptr<T> scenarios that may be impacted by TRIVIAL_ABI.

The previous CL at https://crrev.com/c/3308505 added the TRIVIAL_ABI
attribute to raw_ptr<T> without adding any tests, because the
performance impact cannot be tested in the short-term (before
std::vector starts to use memcpy for such types).  At the same time,
basic correctness smoke tests for affected scenarios are already
possible and desirable - this CL tries to add such tests.

Bug: 1073933, 1275668
Change-Id: I95ac5bdf50131f3cba4a2eb0e6cfd9ebd891bfe4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3313460
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/main@{#948589}