Add SkSLInterfaceBlock.cpp.

This lets us move some of the bulky code out of the header.

Change-Id: Ie12779601395f461b53912f82736d02edb7dd6c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/592537
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Arman Uguray <armansito@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
5 files changed