heap: Move feature flags from RuntimeEnablesFeature to Blink common

This moves all garbage collection features into Blink's common features
bottleneck as these features
- do not require IDL support
- are not flipped for tests only but always fully enabled
- often require Finch support which is not directly supported for
  RuntimeEnabledFeatures

Change-Id: Icf5dfcdfcee3169560f133e5e77b4442fd813fb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1692405
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675599}