Separate IRGenerator and Compiler into separate DSLWriter fields.

The only actual use of Compiler is in dsl::ReleaseProgram. All other
uses of Compiler in DSLWriter were to gain access to its internal
IRGenerator.

Change-Id: I0169cb1debf837894b1be3321f3d920259f7e91a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/451741
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
3 files changed