Counters in generated code, as enabled with --native-code-counters, do not work
in the snapshot. This adds a `v8_enable_snapshot_code_counters` build option
enabled by defaut in debug mode that allows code from the snapshot to increment
the current isolate's set of counters.

For this to work, we need to add native code counters in the external reference
table.

To keep the no snapshot configuration similar, we've also enabled the
--native-code-counters flag by default for debug builds.

Change-Id: I4478b79858c9b04f57e06e7ec67449e9e3a76f53
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1528998
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60495}