test-embedder-tracing.cc -> embedder-tracing-unittest.cc

In addition
- Add heap helpers
- CHECK -> EXPECT macros

Bug: v8:12781
Change-Id: Ibd17a4e6d527c963170af54c57f6abc51cb08808
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3576127Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79883}