GLSL supports casting vec4 into mat2 and vice versa, so SkSL should have
equivalent support. This CL allows the Compound constructor to take a
matrix as input, and fixes up backends to do the right thing when a
matrix shows up in the compound-constructor path.
Change-Id: I13289ad0a27ba59bddc3706093820594efebc693
Bug: skia:12067
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/426003
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
