feat: resolve inherent and implemented associated items in docs
This partially fixes#9694.
Supported:
- Trait methods and constants.
* Due to resolution differences pointed out during the review of the PR, trait associated types are _not_ supported.
- Inherent methods, constants and associated types.
* Inherent associated types are a [nightly feature](https://github.com/rust-lang/rust/issues/8995), and are supported with no additional work in this PR.
Screenshot of VS Code running with the change:
<img width="513" alt="image" src="https://github.com/rust-lang/rust-analyzer/assets/7189784/c37ed8b7-b572-4684-8e81-2a817b0027c4">
You can see that the items are resolved (excl. trait associated types) since they are semantically highlighted in the doc comment.
c3c07c66d3