SkSL::Operator was previously just a thin wrapper around Token::Kind and
everything was therefore written in terms of Token. Since Token is not
accessible from include/ (and we don't want it to be), this creates an
actual Operator enum and eliminates the dependence on Token. This will
enable followup changes to reference Operator from within the DSL
include files.
Change-Id: I49555c9151618fd15970a303d2284972c78c3f21
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/525976
Reviewed-by: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
