Rollup merge of #138090 - yotamofek:pr/rustdoc/flatten-ifs, r=GuillaumeGomez

`librustdoc`: flatten nested ifs

Some minor cosmetic improvements (IMHO) found while working on something else.
But reviewed with [no whitespace](https://github.com/rust-lang/rust/pull/138090/files?diff=unified&w=1).

Author: compiler-errors