Rollup merge of rust-lang#114021 - GuillaumeGomez:session-time-docs, r=lcnr

Add missing documentation for `Session::time`

r? `@lcnr`

Author: matthiaskrgr

compiler/rustc_session/src/utils.rs

@@ -7,6 +7,7 @@ impl Session {
     pub fn timer(&self, what: &'static str) -> VerboseTimingGuard<'_> {
         self.prof.verbose_generic_activity(what)
     }
+    /// Used by `-Z self-profile`.
     pub fn time<R>(&self, what: &'static str, f: impl FnOnce() -> R) -> R {
         self.prof.verbose_generic_activity(what).run(f)
     }