Move GrSmallPathAtlasMgr to its own file and out-line

There are no intentional behavioral changes in this CL. It should
purely be cut, paste, re-shuffle & get re-compiling.

Bug: 1108408
Change-Id: Ic8457d0af76861f2ea881177f2b2c0fe0bf85146
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/309040
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
4 files changed