Add transparent version of std::equal_to<> and std::hash<> for raw_ptr

In order to have heterogenous key support with absl::flat_hash_set<>,
write version of std::equal_to<> and std::hash<> that are transparent
and work with raw_ptr<T, RawPtrTraits>.

Bug: 477014186, 453998692
Change-Id: I1e990e057dc208b6325aa8db707bc91b520e159d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7511026
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Benoit Lize <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1575187}
NOKEYCHECK=True
GitOrigin-RevId: 21c36ff02badbe6eee1f72325f5188fdd5943bb8