metal: support (simulated) visionOS

[jinleili]

Checklist

• Run cargo clippy.
• Run cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Description
Apple announced the new visionOS at WWDC 2023. Now, visionOS 1.0 can be run on Xcode 15 Beta 2 through the simulator. This pull request addresses a bug that occurs when running wgpu on visionOS.

The MSL version was determined based on the iOS and macOS versions. The following error occurs when running the boids example:

Using Apple xrOS simulator GPU (Metal)
[2023-06-22T07:41:49Z ERROR wgpu::backend::direct] Handling wgpu errors as fatal by default
thread '<unnamed>' panicked at 'wgpu error: Validation Error

Caused by:
    In Device::create_compute_pipeline
      note: label = `Compute pipeline`
    Internal error: MSL: UnsupportedAddressSpace(Storage { access: StorageAccess(LOAD) })

', /Users/lijinlei/Rust/forks/wgpu/wgpu/src/backend/direct.rs:3023:5

In addition, the family_check field was also set based on the iOS and macOS versions, which causes feature detection to fail on visionOS. The following error occurs when running the shadow example:

-[MTLDebugRenderCommandEncoder validateCommonDrawErrors:]:5780: failed assertion `Draw Errors Validation

Vertex Function(vs_bake): the offset into the buffer u_entity that is bound at buffer index 1 must be a multiple of 256 but was set to 128.
'

Testing
Tested via https://github.com/jinleili/wgpu-in-app

720p.mp4

[teoxoy]

I can't yet find any info on visionOS in the Metal Feature Set Tables. I feel like it might be too early for this but if people want to play with it I'm not opposed to it.