Change the TPH API so that it uses v8::internal::Isolate rather
than v8::isolate.

The third party heap is within the internal namespace and ultimately
needs access to v8::internal::Isolate to do things such as adding code
ranges.  There's no reason for it to use v8:Isolate.

Bug: v8:9533
Change-Id: I8c3ecd6278081f03133013d4e3b02fb3ed228baf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2036088Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Steve Blackburn <steveblackburn@google.com>
Cr-Commit-Position: refs/heads/master@{#66113}