Remove unsafe compiler methods related to external values

We don't want to be polluting the global namespace with external values,
especially when the typical/recommended way to use the Compiler is with
a single long-lived instance. Force client code to manage ownership (the
only non-unit-test case was already doing this), and pass external
values to convertProgram, so they can be added to the Program's symbol
table.

Change-Id: If4c1db5e48a62e2cf4333b8d80420f2dfede27ab
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319125
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
6 files changed