make all instructions take two-way labels

This turned out to be quite an easy transformation
with yesterday's work already done.  No codegen changes.

Change-Id: Ife19ab7731514c54cfed963a6d2e9b1ec2246997
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/227137
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
3 files changed