DSLVar is normally implicitly converted to DSLExpression wherever it is
used, but the naively template-ized nature of DSLFunction::operator()
meant that it was accepting DSLVar parameters directly. Since DSLVar is
non-copyable, this meant DSLVar couldn't be passed directly to a DSL
function.
The smarter templates in this change are able to pass DSLVar by
reference.
Change-Id: Id04531f909cefd29b377c46e37fc4525bb29953c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/394161
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
80f6235688