Previously ExternalValues were flexible, and could be used as raw values
(with the ability to chain access via dot notation), or they could be
callable. The only non-test use-case has been for functions (in
particles) for a long time. With the push towards SkVM, limiting
ourselves to this interface simplifies things: external functions are
basically custom intrinsics (and with the SkVM backend, they'll just get
access to the builder, and be able to do any math, as well as
loads/stores, etc).
By narrowing the feature set, we can rename everything to reflect that,
and it's overall clearer (the SkSL types now mirror FunctionReference
and FunctionCall directly, particularly in how they're handled by the
CFG and inliner).
Change-Id: Ib5dd34158ff85aae6c297408a92ace5485a08190
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/350704
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
be0b3b7363