WIT linting

While discussing the design of WIT it has occasionally been suggested that certain things should be discouraged without being forbidden. Some examples:

- Referencing a `@deprecated` type
- Using deprecated WIT features
- Common reserved keywords as labels (`new`, `yield`, `assert`, etc.) which can require awkward and confusing name mangling in some language bindings
- Patterns that are expected to conflict with future features, like (proposed) [resource properties](https://github.com/WebAssembly/component-model/issues/235)

This could be handled by a linting tool, which might look like:

- A new `wit-bindgen lint` subcommand
- Some mechanism to suppress specific lints, like a new WIT annotation e.g. `@allow(common-reserved-labels)`