Represent splat constructors with a dedicated ConstructorSplat class.

Change-Id: Ic9c3d688b571591d057ab6a4e998f1f9712a1b58
Bug: skia:11032
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/392117
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
19 files changed