Revert "Disallow matrix ctors which overflow a column."

This reverts commit eb68973c2f5ac8f8dd169037cfc32885a024448d.

Reason for revert: ES2 conformance test checks this

Original change's description:
> 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>

Bug: skia:12443
Change-Id: I5a32744c88b9b830ad657488824c8c7dd0b0a652
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/458056
Commit-Queue: John Stiles <johnstiles@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
26 files changed