Auto merge of #99918 - WaffleLapkin:fnFnfun, r=estebank

Recover wrong-cased keywords that start items

(_this pr was inspired by [this tweet](https://twitter.com/Azumanga/status/1552982326409367561)_)

r? `@estebank`

We've talked a bit about this recovery, but I just wanted to make sure that this is the right approach :)

For now I've only added the case insensitive recovery to `use`s, since most other items like `impl` blocks, modules, functions can start with multiple keywords which complicates the matter.

diff --cc compiler/rustc_ast/src/token.rs
Simple merge

diff --cc compiler/rustc_parse/src/parser/expr.rs
Simple merge

diff --cc compiler/rustc_parse/src/parser/item.rs
Simple merge

diff --cc compiler/rustc_parse/src/parser/mod.rs
Simple merge

diff --cc compiler/rustc_parse/src/parser/ty.rs
Simple merge