We used to use the Binding decoration for this, but this method is
hopelessly broken. If no explicit MSL resource remapping exists, we
remap automatically in a manner which should always "just work".
This gets rather complicated because MSL does not support OpArrayLength
natively. We need to pass down a buffer which contains buffer sizes, and
we compute the array length on-demand.
Support both discrete descriptors as well as argument buffers.
Change aux buffer to swizzle buffer.
There is no good reason to expand the aux buffer, so name it
appropriately.
Make the code cleaner by emitting a straight pointer to uint rather than
a dummy struct which only contains a single unsized array member anyways.
This will also end up being very similar to how we implement swizzle
buffers for argument buffers.
Do not use implied binding if it overflows int32_t.
This is necessary to deal with indirect draws, where the draw parameters
are given in a buffer instead of passed by the CPU. For normal draws,
the draw parameters are set with Metal's `setVertexBytes:` method.
This undoes the change to add the vertex count to the aux buffer,
rendering that entire discussion largely moot. Oh well. It was a
discussion that needed to happen anyway.
In the past, SPIRV-Cross threw an error in this case because it couldn't
work out which swizzle from the auxiliary buffer needs to be passed.
Now, we pass the swizzle around with the texture object, like a combined
image-sampler and its associated sampler.
It'll be useful to have an "auxiliary buffer" for other builtins--e.g.
`DrawIndex` (which should be easier to implement now), or `ViewIndex`
when someone gets around to implementing multiview.
Pass this buffer to leaf functions as well.
Test that we handle this for integer textures as well.
