The flag --trace-ignition-dispatches has been broken for a long time,
since it was not designed to work with bytecode handlers that are
generated ahead of time by mksnapshot. This splits the existing
--trace-ignition-dispatches logic into two separate parts:

1. A gn argument which instructs mksnapshot to include dispatch counting
   in the bytecode handlers, and ensures that the Interpreter allocates
   the array of counters, and
2. A runtime flag which enables the ignition-statistics extension which
   implements the JS-accessible function getIgnitionDispatchCounters().

Change-Id: I89323425697f5641451f67b9ddcc0303b8ca209f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2937564Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#74992}