This also extracts the {FrontendChannelImpl}, the {SetTimeoutTask}, and
the {SetTimeoutExtension} for reuse by the inspector fuzzer.

R=szuend@chromium.org

Bug: chromium:1142437
Change-Id: I75e49d6fbb4b801ace1ffc9cac963d6b83c52f36
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2505717Reviewed-by: Simon Zünd <szuend@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70909}