... in addition to existing Xxx::yyy().

The idea is to use these getters in hot C++ code since passing isolate
explicitly makes it trivial to compute isolate root value and reduces
the C++ code size.

For full-pointer mode the unused isolate argument will be optimized
away by the compiler, so full-pointer mode should not be affected
in any sense.

Bug: v8:9353
Change-Id: If6c43e3d5b3cbfc0db8b9eccee49dd8c4d168822
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1674035Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62348}