Fix reference definition labels for backtick-quoted shortcut links (#16035)
## Summary
Resolves #16010.
The changes boil down to something like this:
```diff
-/// The [FastAPI documentation] recommends the use of [`typing.Annotated`]
+/// The [FastAPI documentation] recommends the use of [`typing.Annotated`][typing-annotated]
-/// [typing.Annotated]: https://docs.python.org/3/library/typing.html#typing.Annotated
+/// [typing-annotated]: https://docs.python.org/3/library/typing.html#typing.Annotated
```
## Test Plan
Mkdocs:

GitHub:
> ## Why is this bad?
> The [FastAPI documentation] recommends the use of
[`typing.Annotated`][typing-annotated]
>
> ...
>
> [FastAPI documentation]:
https://fastapi.tiangolo.com/tutorial/query-params-str-validations/?h=annotated#advantages-of-annotated
> [typing-annotated]:
https://docs.python.org/3/library/typing.html#typing.Annotated
[CommonMark
dingus](https://spec.commonmark.org/dingus/?text=%23%23%20Why%20is%20this%20bad%3F%0AThe%20%5BFastAPI%20documentation%5D%20recommends%20the%20use%20of%20%5B%60typing.Annotated%60%5D%5Btyping-annotated%5D%0A%0A...%0A%0A%5BFastAPI%20documentation%5D%3A%20https%3A%2F%2Ffastapi.tiangolo.com%2Ftutorial%2Fquery-params-str-validations%2F%3Fh%3Dannotated%23advantages-of-annotated%0A%5Btyping-annotated%5D%3A%20https%3A%2F%2Fdocs.python.org%2F3%2Flibrary%2Ftyping.html%23typing.Annotated):
```html
<h2>Why is this bad?</h2>
<p>The <a href="https://fastapi.tiangolo.com/tutorial/query-params-str-validations/?h=annotated#advantages-of-annotated">FastAPI documentation</a> recommends the use of <a href="https://docs.python.org/3/library/typing.html#typing.Annotated"><code>typing.Annotated</code></a></p>
<p>...</p>
```