move positions to vertex filler
move positions to vertex filler

Creating the position arrays and source bounds was common to many
SubRuns. Collect all this common code into the
TransformedMaskVertexFiller.

Change-Id: Ib3be8a2451759ed8f987c591014aa9d471df0281
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/514218
Reviewed-by: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>
Commit-Queue: Herb Derby <9e12a3d2bbf73546e47cc9958f6ba8f3215b7eaf@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia