Auto merge of #37247 - jseyfried:future_proof_no_link, r=nrc

macros: Future proof `#[no_link]`

This PR future proofs `#[no_link]` for macro modularization (cc #35896).

First, we resolve all `#[no_link] extern crate`s. `#[no_link]` crates without `#[macro_use]` or `#[macro_reexport]` are not resolved today, this is a [breaking-change]. For example,
```rust
```
Any breakage can be fixed by simply removing the `#[no_link] extern crate`.

Second, `#[no_link] extern crate`s will define an empty module in type namespace to eventually allow importing the crate's macros with `use`. This is a [breaking-change], for example:
```rust
mod syntax {} //< This becomes a duplicate error.
```

r? @nrc

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