lang/v8: update to 15.5.35.20 (Chrome 155 stable)

• Enable Temporal. GN can only build the temporal_capi Rust crate with the Chromium Rust toolchain, so build it with cargo as a static library through a small wrapper crate (temporal_capi is no_std) and have GN link that. Crate versions follow Chromium's Cargo.lock. Time zone data is read from devel/icu; use the accessors libicuuc exports instead of ICU's internal udatamem.h, which is not installed.
• Use libclang and its Python bindings from the llvm port for the new metagen instance-types generator, and work around Cursor being unhashable in the bindings before LLVM 21.
• Ignore check_includes_strict, which devel/gn does not know yet.
• Add the licenses of the statically linked crates.
• Depend on libicuuc.so, which is what gets linked, instead of libicudata.so, and stop depending on glib, which was never linked.
• Drop DIST_SUBDIR; distfile names have been unique since the switch to the GitHub mirror.