Implement determinant() in SkSL ES3 public API.

The prototype has been added sksl_public, compile-time optimization is
implemented, and test code has been improved.

Change-Id: I536d6bd7fcae437a03744941b008940bf2a3b1c1
Bug: skia:12202
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/440524
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
8 files changed