build programs lazily in SkVMBlitter

When run over all GMs, this cuts the number of programs
we build and JIT from 531,012 down to 141,930.

Draws the same, of course.

Change-Id: Ia804ded23496a2f534fb94d047547c9b644f3cfc
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/232776
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed