Remove borrowed types from WIT-generated types on the guest

[philpax]

Our version of wit-bindgen generates borrowed types where possible, which leads to significant boilerplate for converting types back and forth:

• https://github.com/AmbientRun/Ambient/blob/main/guest/rust/api/src/internal/component/traits.rs
• https://github.com/AmbientRun/Ambient/blob/main/crates/wasm/src/shared/borrowed_types.rs

Luckily, the lovely folks over at the Bytecode Alliance have fixed this with a recent PR. Once this issue is fixed, we should be able to update and drop all of the borrowed types tooling on the guest (and hopefully not long after, the host).