Deduplicate autoroller docs. Leave them centralized in ANGLEWrangling.md, link to them from BranchingAndRolling.md, and add the Chromium-into-ANGLE autoroller. Bug: angleproject:6323 Change-Id: I913954b92dbe3545320e662de122daf26140d425 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3124341 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Kenneth Russell <kbr@chromium.org>