Slim down GrFragmentProcessor::TextureSampler and GrPrimitiveProcessor::TextureSampler

I'm gearing up to add a GrBackendFormat to GrPrimitiveProcessor::TextureSampler so this CL just reduces the API surface area I'll need to alter.

The GrFragmentProcess::TextureSampler changes just keep it aligned with its "twin".

Change-Id: Ia9ece03ca76b4f6c8ebdaf0e0ba0061ecde6c5f4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248558
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed