Report the total size of global handles in GetHeapStatistics as well.
This size includes used and free global handles.

Change-Id: I08c0647d993a810a37ae9f332732de9551b5ea8d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2083020
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66562}