Hook up ShaderErrorHandler in the Metal backend.

Also cleans up dumping of shader code to use GrShaderUtils.

Change-Id: I4d2a13e1a54284d7da0242b74cebb3900921fc35
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/337077
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
7 files changed