Simplify matrix uniform data management.

We can use `if constexpr` to avoid the need for a helper function that
uses template specialization, and we can use `getBufferPtrAndMarkDirty`
instead of performing the equivalent operations by hand.

Change-Id: I548c719bae4f215e0a9c658a942deaec38ce27ad
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/462098
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed