Abseil LTS 20250512.2

What's New:

The polyfill types absl::any, absl::optional, and absl::variant are now aliases for std::any, std::optional, and std::variant in all builds. (Note that the polyfill implementation absl::string_view remains at the present time, but it defaults to being an alias std::string_view in all builds.)
Added absl::FastTypeId<Type>(), which evaluates at compile-time to a unique id for the passed-in type.
Added absl::endian and absl::byteswap polyfills (25bce12).

Abseil now requires at least C++17 and follows Google's Foundational C++ Support Policy. See this table for a list of currently supported versions compilers, platforms, and build tools.
Nullability template types are deprecated and will be removed in a future release. The macro-style annotations (absl_nonnull, absl_nullable) should be used instead (caf854d).

Baseline: bc257a8
Cherry-pick: 76bb243 (Patch 1)
Cherry-pick: 7313246 (Patch 2)