Abstracting over arrays

[MaikKlein]

• spir-v differentiates between runtime arrays and static arrays

• Slices can't be supported in rlsl at the moment

• Things like len on a static array currently maps to Slice::len() in Rust, which can't be expressed.

• Const generics aren't a thing yet.

Because slices are not supported, we need to abstract over arrays with generics

fn foo(arr: &impl Array<f32>) { .. }