To improve ergonomics, graph generation is now triggered by the
IfBuilder0 destructor instead of requiring an implicit call to
Build().  This will be more expected for gasm users, since no other
builders require such a Build() call.

Drive-by: Rename 'ForSmiZeroUntil' methods to 'ForZeroUntil' since
'Smi' doesn't make sense in this context (TF only knows the Number
type here).

Bug: v8:9972
Change-Id: I365805e8428b35f19760e6ff155423463194b0f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011107
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65877}