Rename SoftwarePathAtlas to RasterPathAtlas.

Also moves RasterPathAtlas to its own file, since it'll be expanded
and get more complex.

Bug: b/291735945
Change-Id: Ie4384022950294497e65af26df6a7679a7d789b5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/761596
Reviewed-by: Arman Uguray <armansito@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
10 files changed