deps: V8: cherry-pick 64b36b441179

[rmagrin]

Cherry-picks V8 commit 64b36b441179 (ASCII fast path optimization in WriteUtf8V2).

This optimizes the WriteUtf8V2 path for ASCII-only one-byte strings by using SIMD-accelerated validation (simdutf::validate_ascii) followed by a bulk memcpy, instead of encoding byte-by-byte through the generic UTF-8 path.

Changes:

• deps/v8/src/strings/unicode-inl.h — Added IsAsciiOneByteString template specializations and ASCII fast path in Encode
• deps/v8/src/strings/unicode.h — Added IsAsciiOneByteString declarations
• common.gypi — Incremented embedder string (-node.11 → -node.12)

References:

• V8 commit: v8/v8@64b36b4
• Chromium review: https://chromium-review.googlesource.com/c/v8/v8/+/7124103
• Supersedes: deps: V8: cherry-pick 64b36b441179 #61698 (was against v24.x-staging, maintainers requested rebase to main)

[nodejs-github-bot]

Review requested:

• @nodejs/gyp
• @nodejs/security-wg
• @nodejs/v8-update

[RafaelGSS]

The patch seems to be breaking CI https://github.com/nodejs/node/actions/runs/21768460714/job/62821066535?pr=61712

[targos]

In file included from ../../deps/v8/src/runtime/runtime.h:14,
                 from ../../deps/v8/src/codegen/external-reference.h:9,
                 from ../../deps/v8/src/codegen/external-reference-table.h:11,
                 from ../../deps/v8/src/execution/isolate-data.h:10,
                 from ../../deps/v8/src/execution/isolate.h:33,
                 from ../../deps/v8/src/api/api.h:18,
                 from ../../deps/v8/src/api/api.cc:5:
../../deps/v8/src/strings/unicode.h:218:13: error: explicit specialization in non-namespace scope 'class unibrow::Utf8'
  218 |   template <>
      |             ^
../../deps/v8/src/strings/unicode.h:219:15: error: template-id 'IsAsciiOneByteString<uint8_t>' in declaration of primary template
  219 |   inline bool IsAsciiOneByteString<uint8_t>(const uint8_t* buffer, size_t size);
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../deps/v8/src/strings/unicode.h:221:13: error: explicit specialization in non-namespace scope 'class unibrow::Utf8'
  221 |   template <>
      |             ^
../../deps/v8/src/strings/unicode.h:222:15: error: template-id 'IsAsciiOneByteString<uint16_t>' in declaration of primary template
  222 |   inline bool IsAsciiOneByteString<uint16_t>(const uint16_t* buffer,
      |               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ninja: build stopped: subcommand failed.
make: Leaving directory '/home/runner/work/_temp/node-v26.0.0-nightly2026-02-07702401a1af-slim'