- Removes the unused Worklist implementation. All uses now refer to
  ::heap::base::Worklist.
- Renames CppgcWorklistTest -> WorklistTest
- Add test for Swap()

Bug: v8:12426
Change-Id: I62c3472c030b853a846cf13ab48597ea1af8f700
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306507Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78208}