[hal] Do not expose dependency on metal and objc crates

[madsmtm]

Connections
Allows #5641 to not contain breaking changes.

Description
wgpu-hal's dependency on the metal and objc crates is currently indirectly exposed via. the parameter types on hal::metal::Surface::from_view, hal::metal::Surface::from_layer and hal::metal::Instance::create_surface_from_layer.

This is unfortunate, since it ties wgpu-hal to specific dependencies, and specific versions of said dependencies. Instead, this PR changes these methods to use NonNull<c_void>, and prefers to instead document which type the user is expected to pass here. This mirrors the top-level API already exposed in Instance::create_surface_metal.

Additionally, this PR removes metal::Instance::create_surface_from_layer, since it was only a simple wrapper, and splits metal::Surface::from_view into from_ns_view and from_ui_view to make it clearer/easier to document what the requirements are for the given type. This matches raw_window_metal::Layer's methods.

Testing
Tested using:

# macOS
cargo run --bin wgpu-examples -- cube

# iOS on Mac Catalyst using Cargo Bundle
echo "[package.metadata.bundle]" >> examples/features/Cargo.toml
cargo bundle --format=ios --target=aarch64-apple-ios-macabi --bin wgpu-examples
./target/aarch64-apple-ios-macabi/debug/bundle/ios/wgpu-examples.app/wgpu-examples cube

I believe this should suffice, as this mostly modifies the entry point to surface creation.

Checklist

• Run cargo fmt.
• Run taplo format.
• Run cargo clippy --tests. If applicable, add:
  • --target wasm32-unknown-unknown
• Run cargo xtask test to run tests.
• If this contains user-facing changes, add a CHANGELOG.md entry.