This migrates all remaining uses of cImport (and addTranslateC for good
measure) to using translate-c for C translation, ensuring that we are
ready for when cImport is removed from the language, and also that all
sources of C translation are using the same snapshot of the external
package (when can then be updated when we need to fix something).
A couple of notes:
* A few options have been added to support the new translations, namely
the ability to link libraries (passed through to linkLibrary on the
Translator side) and whether or not to initialize default values
(looks like cImport did this without a way to control it, but
translate-c does not do it by default).
* Using the new library linking option actually simplifies the process
of translating a number of the C packages as we have been shipping the
necessary headers for these packages already with the applicable
libraries. For some of the more complex translation processes though,
we still include the appropriate directories directly.
The GLSL to MSL conversion process uses a passed-in sampler state for
the `iChannel0` parameter and we weren't providing it. This magically
worked on Apple Silicon for unknown reasons but failed on Intel GPUs.
In normal, hand-written MSL, we'd explicitly create the sampler state as
a normal variable (we do this in `shaders.metal` already!), but the
Shadertoy conversion stuff doesn't do this, probably because the exact
sampler parameters can't be safely known.
This fixes a Metal validation error when using custom shaders:
```
-[MTLDebugRenderCommandEncoder validateCommonDrawErrors:]:5970: failed
assertion `Draw Errors Validation Fragment Function(main0): missing Sampler
binding at index 0 for iChannel0Smplr[0].
```
