Add raw_handle method for metal texture

[ericszentivanyi]

Connections

• Proposal for Underlying Api Interoperability #4067
• Closes raw_handle method for Metal texture in wgpu-hal #6891

Description
The problem was that a raw Metal texture was inaccessiable whereas a Vulkan texture could be with the raw_handle method. To fix this, I've implemented the raw_handle method which returns a reference to a metal::Texture.

Once a &metal::Texture is received through the method, it can be used through .clone to prevent a lifetime error and because metal::Texture does not implement the Copy trait as opposed to vk::Image.

Testing

Example:

let raw_texture = unsafe {
  texture.as_hal::<wgpu_hal::api::Metal, _, _>(|texture| {
    texture.unwrap().raw_handle().clone()
  })
};

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.
• Add change to CHANGELOG.md. See simple instructions inside file.

[cwfitzgerald]

Thanks!