Add a new gm for large kernel matrix convolution

As a precursor to 263495, we need test coverage for this.

According to Skia Gold, the current matrix convolution implementation test is showing very different results on CPU & GPU. On the CPU, the last test case turns blue! See closest negative here: https://gold.skia.org/search?fdiffmax=-1&fref=false&frgbamax=255&frgbamin=0&head=true&include=false&limit=50&master=false&match=name&metric=combined&neg=true&new_clstore=true&offset=0&pos=true&query=cpu_or_gpu%3DGPU%26name%3Dmatrixconvolution_color%26source_type%3Dgm&sort=desc&unt=true

Change-Id: I4569e0fd0ec953dc75dbb99516d69741514efb60
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264517
Auto-Submit: Adlai Holler <adlai@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed