Reland "Merge ScopedFakeClock and ScopedBaseFakeClock"

This reverts commit 1c9a7db60246006724e91677e341fbc3e5f34892.

Reason for revert: downstream tests migrated

Original change's description:
> Revert "Merge ScopedFakeClock and ScopedBaseFakeClock"
>
> This reverts commit 48c80a6549f5d21feb33aafa9c5c440879b2eaf5.
>
> Reason for revert: breaks downstream
>
> Original change's description:
> > Merge ScopedFakeClock and ScopedBaseFakeClock
> >
> > Their implementation is almost identical. Only 'InvokesInDelayOrder'
> > test relied on extra behavior of the ScopedFakeClock. This test is
> > adjusted to call 'ProcessAllTasks' itself instead of relying on
> > 'ScopedFakeClock' to do so for it.
> >
> > Bug: webrtc:42223992
> > Change-Id: I5221ee76fec11315846649bb84dd4098451a8b80
> > Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/478382
> > Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
> > Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> > Cr-Commit-Position: refs/heads/main@{#47904}
>
> Bug: webrtc:42223992
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Change-Id: I173441e27a66adbaa99335ea6b59a3d5e3b67fc5
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/478841
> Commit-Queue: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
> Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
> Auto-Submit: Danil Chapovalov <danilchap@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#47907}

Bug: webrtc:42223992
Change-Id: I5791afa93651e4b84d091f07d6449aabd69bbcb9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/479840
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47932}