Rollup merge of #91571 - dtolnay:printerderef, r=Mark-Simulacrum

Remove unneeded access to pretty printer's `s` field in favor of deref

I found it taxing in some of my recent PRs touching the pretty printer to maintain consistency with the surrounding code, since the current code is all over the place about whether it uses `self.s.…()` or `self.…()` for invoking methods of `rustc_ast_pretty::pp::Printer`.

This PR standardizes on `self.…()` — relying on the `Deref` and `DerefMut` impls introduced by [#62532](cab4532).

Author: matthiaskrgr