Add should_pause to V8StackTraceId in preparation for
async stepping simplification [1].

[1] https://chromium-review.googlesource.com/c/v8/v8/+/1783724

BUG=chromium:1000475
TBR=yangguo@chromium.org

Change-Id: I3a90d33322c83f624a3d28c18ebdfff80b2cd904
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1799453Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63696}