Convert IRGenerator::convertDo to DoStatement::Make.

We currently don't have any optimizations for do-statements so the
primary benefit is moving code out of IRGenerator.

Change-Id: Ibc4d1ecd87ebef572e742dfdb15821cf4ac0f047
Bug: skia:11342
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376179
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
8 files changed