add test cases for TypedBuffer

[SiebenCorgie]

Adds 3 test cases for the TypedBuffer interface. Currently typed-buffer-unbound & typed-buffer-unbound-struct are broken with:

error: cannot cast between pointer types

test [ui] ui/storage_class/typed-buffer-unbound.rs ... FAILED
normalized stderr:
error: cannot cast between pointer types
       from `*struct core::mem::MaybeUninit<&mut [MyData]> { uninit: *[struct MyData { a: f32, b: [u32; 3] }], value: u32 }`
         to `*struct &mut [MyData] { *[struct MyData { a: f32, b: [u32; 3] }], u32 }`
   --> /home/myname/.rustup/toolchains/nightly-2023-09-30-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/mem/maybe_uninit.rs:570:6
    |
570 |     }
    |      ^
    |
note: used from within `>::as_mut_ptr`
   --> /home/myname.rustup/toolchains/nightly-2023-09-30-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/mem/maybe_uninit.rs:570:6
    |
570 |     }
    |      ^
note: called by ` as core::ops::deref::Deref>::deref`
   --> /home/myname/Code/Rust/git_pulls/rust-gpu/crates/spirv-std/src/typed_buffer.rs:75:39
    |
75  |                 result_slot = in(reg) result_slot.as_mut_ptr(),
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^
note: called by `typed_buffer_unbound_struct::compute`
   --> $DIR/typed-buffer-unbound-struct.rs:18:32
    |
18  |     let mut load_dta: MyData = unsafe { my_data.index(global_invocation_id.x as usize) }[0];
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: called by `compute`
   --> $DIR/typed-buffer-unbound-struct.rs:12:8
    |
12  | pub fn compute(
    |        ^^^^^^^

error: cannot cast between pointer types
       from `*struct core::mem::MaybeUninit<&mut [MyData]> { uninit: *[struct MyData { a: f32, b: [u32; 3] }], value: u32 }`
         to `*struct &mut [MyData] { *[struct MyData { a: f32, b: [u32; 3] }], u32 }`
   --> /home/myname.rustup/toolchains/nightly-2023-09-30-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/mem/maybe_uninit.rs:570:6
    |
570 |     }
    |      ^
    |
note: used from within `>::as_mut_ptr`
   --> /home/myname/.rustup/toolchains/nightly-2023-09-30-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/mem/maybe_uninit.rs:570:6
    |
570 |     }
    |      ^
note: called by ` as core::ops::deref::DerefMut>::deref_mut`
   --> /home/myname/Code/Rust/git_pulls/rust-gpu/crates/spirv-std/src/typed_buffer.rs:95:39
    |
95  |                 result_slot = in(reg) result_slot.as_mut_ptr(),
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^
note: called by `typed_buffer_unbound_struct::compute`
   --> $DIR/typed-buffer-unbound-struct.rs:21:36
    |
21  |     let mut target = unsafe { &mut my_data.index_mut(global_invocation_id.y as usize)[0] };
    |                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: called by `compute`
   --> $DIR/typed-buffer-unbound-struct.rs:12:8
    |
12  | pub fn compute(
    |        ^^^^^^^

error: aborting due to 2 previous errors