Rollup merge of #78962 - poliorcetics:rustdoc-raw-ident-test, r=jyn514
Rollup merge of #78962 - poliorcetics:rustdoc-raw-ident-test, r=jyn514

Add a test for r# identifiers

I'm not entirely sure I properly ran the test locally (I think so though), waiting for CI to confirm. :)

```````@rustbot``````` modify labels: T-rustdoc

r? ```````@jyn514```````

aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust