This adds a new status file indicator "HEAVY" to mark tests with high
resource demands. There will be other tests running in parallel,
but only a limited number of other heavy tests. The limit is
controlled with a new parameter --max-heavy-tests and defaults to 1.

The change also marks a variety of tests as heavy that recently had
flaky timeouts. Heavy also implies slow, hence heavy tests are
executed at the beginning with a higher timeout like other slow tests.

The implementation is encapsulated in the test-processor chain. A
new processor buffers heavy tests in a queue and adds buffered tests
only if other heavy tests have ended their computation.

Bug: v8:5861
Change-Id: I89648ad0030271a3a5af588ecc9c43285b728d6d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2905767
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74712}