With the recent changes to Array#sort, the main algorithm does not
need to bail out anymore. Only the initial copying into the workarray,
as well as the final copying back into the original backing store
might cause a switch from fast-path to the slow-path.

This CL changes the slow-path so sorting itself is not restarted and
the slow-path will continue copying where the fast-path left off.

R=jgruber@chromium.org

Bug: v8:7382
Change-Id: I4ab61daa62bb816f4f6e16e60bde1f948ad1e7db
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1507717
Commit-Queue: Simon Zünd <szuend@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60151}