This CL adds a few transformations that clean up the set of reported
source ranges. Duplicates, empty, and uncovered ranges are removed, and
nested/consecutive ranges are merged if possible.

BUG=v8:6000

Change-Id: I421ee35ce8292cfe84c1eea4f653762cea5d909d
Reviewed-on: https://chromium-review.googlesource.com/558411Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46450}