Implements ProfilerCodeObserver, a class to track the generation and
movement of code on the heap for the lifetime of each CpuProfiler. When
sampling is inactive, logged code is committed directly to the CodeMap.
During profiling, ProfilerCodeObserver redirects these events onto the
profiling thread for later dispatch.

Bug: v8:9151
Change-Id: Ib5b152446d2a3838e1b00a80253fc4fbd2f6e8c3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1604143Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#62943}