Disallow matrix ctors which overflow a column.

The GLSL spec allows matrix constructors containing vectors that would
split between multiple columns of the matrix. However, in practice, this
does not actually work well on a lot of GPUs!

- "cast not allowed", "internal error":
	Tegra 3
	Quadro P400
	GTX 660
	GTX 960
- Compiles, but generates wrong result:
	RadeonR9M470X
	RadeonHD7770

Since this isn't a pattern we expect to see in user code, we now report
it as an error at compile time. mat2(vec4) is treated as an exceptional
case and still allowed.

Change-Id: Id6925984a2d1ec948aec4defcc790a197a96cf86
Bug: skia:12443
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/449518
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
26 files changed