Add a helper method for isolate == v8::Isolate::TryGetCurrent();

Bug: v8:12346
Change-Id: Ibbd1ce1865b0092c8dbcfad5a3bad99fb5858980
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3251173Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Auto-Submit: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77609}