Revert "Rename sampleVariablesSupport() to sampleMaskSupport()"

This reverts commit 766b4c9c21767998d367f22393373bb8a7a70fb2.

Reason for revert: GMs and bots

Original change's description:
> Rename sampleVariablesSupport() to sampleMaskSupport()
> 
> We have only implemented support for the sample mask. Renaming the cap
> to reflect that.
> 
> Change-Id: I10b5923c7464093187336016963a8ac51ebd54f5
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249932
> Commit-Queue: Chris Dalton <csmartdalton@google.com>
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>

TBR=egdaniel@google.com,csmartdalton@google.com,ethannicholas@google.com

Change-Id: I712169e86ee479bffd71d6665710f731d6c0e042
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/250179
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
11 files changed