Move ProgramKind and ProgramSettings types out of SkSL::Program.

This change will allow these types to be forward-declared; C++ doesn't
allow forward declaration of types declared inside a struct. Moving
these types out of Programs resulted in a large diff.

The Settings::Value helper class has been moved inside of the
IRGenerator. In practice, it was actually just an implementation detail
of how IRGenerator looks up caps-values by name. It seems very unlikely
that this will be necessary elsewhere going forward.

Change-Id: I6119417fae608f1c492a27de746d2b550ef8ca20
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/370836
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
43 files changed