way more p-> inference

We can infer the builder on any method that's got at least one I32/F32
argument.  That's basically everything but splat, uniform??, and load??.

This will let us write things like

   sqrt(x*x + y*y)

instead of

   p->sqrt(x*x + y*y)

Previously we had to inherit from skvm::Builder for that...
I think we can remove all that inheritance once I fill all this out.

To make the impl. terser, give I32/F32 an operator-> for their Builder.

Open question about whether to add operator>>?  operator<< is
unambiguous, but operator>> on I32 is probably just going to be
more confusing than sticking with shr and sra.

Change-Id: Id7f1334f87e2354c8733a93d510569df38ae861e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/280318
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
3 files changed