This makes RestoreGeneratorRegisters do a fuller resume process: update
the state register to indicate that it is now executing, and update the
accumulator with the input_or_debug_pos of the generator - i.e., perform
the boilerplate generator resuming in one bytecode instead of several.

Change-Id: Ia87b6766ac023064b40d3e9a143e7b32118ea3a0
Reviewed-on: https://chromium-review.googlesource.com/859770
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50499}