Just a cleanup, should not change behavior, although we will allocate
more handles in some cases.

Also re-orders some of the implementations of the interface to try
and keep things consistent.

Included cleanup: Change CodeEventDispatcher so that it now implements
CodeEventListener, given that it had that exact interface already.
Also remove the macro dispatch to try and make things a bit easier to
read.

Bug: chromium:1033407
Change-Id: Id943b10c49f102d9783d8f4cf3a8c43e04364c77
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1976390Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65571}