rename inner AsFPArgs to stand-alone GrFPArgs

This prepares us to share this with other effects (most notably maskfilters)

Bug: skia:
Change-Id: I12530fdf10c4e5f2a9ab6d394bf9e87c54ea60c4
Reviewed-on: https://skia-review.googlesource.com/97062
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
27 files changed