PersistentHandlesScope works similar to the DeferredHandleScope, but
returns PersistentHandles instead of DeferredHandles on Detach().

Since PersistentHandlesScope takes over filled blocks from the
main thread local handle, remove the block_size_ field and use
kHandleBlockSize instead. This way all blocks have exactly the same size.

Bug: v8:10315
Change-Id: I295cad6f84852f87c55d95572905069443f5698c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2324254
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69138}