Add support for matrix division to Metal codegen.

This CL adds a polyfill for componentwise matrix/matrix division to
Metal, as well as matrix/=matrix. Matrix/scalar and scalar/matrix
division work by splatting the scalar out to a matrix (handled in the
prior CL, http://review.skia.org/407616) and then performing
componentwise matrix/matrix division.

Working demonstration (copy-pasted from the Metal output file):
http://screen/BrqyPcbPrB7Dy4m

Change-Id: I6a8b97783be3485f7ffee551b669d14bc58e7568
Bug: skia:11125
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407796
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed