Rollup merge of #129087 - slanterns:option_get_or_insert_default, r=dtolnay

Stabilize `option_get_or_insert_default`

Closes: https://github.com/rust-lang/rust/issues/82901.

`@rustbot` label: +T-libs-api

r? libs-api

compiler/rustc_session/src/lib.rs

@@ -3,7 +3,6 @@
 #![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(map_many_mut)]
-#![feature(option_get_or_insert_default)]
 #![feature(rustc_attrs)]
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end