Use objc2-metal with metal naming scheme

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`

Another noteworthy thing to mention is that `objc2-metal` does not (yet)
provide a fallback for MTLCopyAllDevices, so we have to do that
ourselves:
madsmtm/objc2@3543940

Author: madsmtm

CHANGELOG.md

@@ -81,6 +81,9 @@ By @brodycj in [#6924](https://github.com/gfx-rs/wgpu/pull/6924).
 - Fix drop order in `Surface`. By @ed-2100 in [#6997](https://github.com/gfx-rs/wgpu/pull/6997)
 - Fix a possible deadlock within `Queue::write_texture`. By @metamuffin in [#7004](https://github.com/gfx-rs/wgpu/pull/7004)
 
+#### Metal
+- Use autogenerated `objc2` bindings internally, which should resolve a lot of leaks and unsoundness. By @madsmtm in [#5641](https://github.com/gfx-rs/wgpu/pull/5641).
+
 #### Vulkan
 
 - Stop naga causing undefined behavior when a ray query misses. By @Vecvec in [#6752](https://github.com/gfx-rs/wgpu/pull/6752).