Create autogenerated reference for all the lints known by rustc

[frewsxcv]

similar to the error index or unstable book

one can get all the lints via lint_store on the session:

rust/src/librustc/session/mod.rs

Line 83 in ae544ee

pub lint_store: RefCell<lint::LintStore>,

we'll probably want to create a new crate in src/tools/ for retrieving the lints and generating markdown, similar to:

• https://github.com/rust-lang/rust/tree/master/src/tools/unstable-book-gen
• https://github.com/rust-lang/rust/tree/master/src/tools/error_index_generator

[zackmdavis]

duplicate of #49416?

[frewsxcv]

yep! good call