Provide a stub `third_party_heap::Heap` implementation to work around
linker erors with Visual Studio.

cl.exe in debug mode seems to eliminate dead code not as aggressively
as clang or gcc, resulting in references to `third_party_heap::Heap`
remaining in unreachable code paths.

Refs: https://github.com/bnoordhuis/v8-cmake/issues/10
Bug: v8:10427
Change-Id: I61fde11697adc663b182f60c132eda435a7f11bd
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2159490
Commit-Queue: Ben Noordhuis <info@bnoordhuis.nl>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Auto-Submit: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67293}