Adds the notion of a "source type" to CpuProfileNode instances, hinting
at the underlying source of the function or state that resulted in the
generation of the node.

Bug: v8:9001
Change-Id: Ie14c54d41b99eb02f54b423fa5d939e9d7f63785
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1510576
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60590}