Auto merge of #22466 - Kimundi:str_pattern_ai_safe, r=aturon

This is not a complete implementation of the RFC:

- only existing methods got updated, no new ones added
- doc comments are not extensive enough yet
- optimizations got lost and need to be reimplemented

See https://github.com/rust-lang/rfcs/pull/528

Technically a

[breaking-change]

diff --cc src/librustc/lint/builtin.rs
Simple merge

diff --cc src/librustc/session/mod.rs
Simple merge

diff --cc src/librustc_driver/pretty.rs
Simple merge

diff --cc src/libstd/old_path/windows.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge