add per-program control over JIT

We have a global flag controlling whether skvm::Programs JIT,
and this adds a per-Program flag to skvm::Builder::done().

Use it for single-color color filtering, and add a unit test.

Change-Id: I3a87761c8c6b818111d03c97b31f8b30d9f2c194
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/367856
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
4 files changed