[cctest] Add fuzz tests for generating parallel moves.

These new tests are somewhat similar to the existing gap resolver tests except
we use the code generator and eventually run the generated code. The main idea
is to cover cases that are difficult to hit, such as move from/to slots which
are out of range of loads and stores, but may happen nonetheless.

At this time, the tests only make sure the code generator actually generated
some code, and that this code runs. In the future, it would be great to also
check that the moves were actually performed.

Bug: v8:6553
Change-Id: I089a25fa05b3a20649658bb8952926ab11f91d68
Reviewed-on: https://chromium-review.googlesource.com/574850
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47733}