`tint::Program` will become the new public API object for a parsed shader program.
For now, have Program be a simple wrapper around ast::Module so we can migrate Dawn's use of the public tint API.
Add new Program variants of public APIs for places that returned or took a Module.
Remove Reset() methods from Generators, they aren't used, and make the migration harder.
Change-Id: Ic5bee46ceb109ea591ba7fec33685220b244a1ae
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/38540
Reviewed-by: dan sinclair <dsinclair@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>