To keep the diff smaller and easier to review, this uses a temporary
fork of `objc2-metal` and `objc2-quartz-core` whose methods use the
naming scheme of the `metal` crate.

One particular difficult part with this is that the `metal` crate has
several methods where the order of the arguments are swapped relative
to the corresponding Objective-C methods.

This includes most perilously (since these have both an offset and an
index argument, both of which are integers):
- `set_bytes`
- `set_vertex_bytes`
- `set_fragment_bytes`
- `set_buffer`
- `set_vertex_buffer`
- `set_fragment_buffer`
- `set_threadgroup_memory_length`

But also:
- `set_vertex_texture`
- `set_fragment_texture`
- `set_sampler_state`
- `set_vertex_sampler_state`
- `set_fragment_sampler_state`