Add MakeSpecialType to replace several one-off Type factories

An upcoming change adds more of these "special" types, this pattern
seems just as easy to follow?

Change-Id: Ib652c8f11a98d33c14300294e521a1378345bc2d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/392379
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed