Improve clippy, and add more docs (#3306)

* Silence a few clippy warnings

* Use named threads

* Remove some deprecated functions

* Document Context and Ui fully

* Use `parking_lot::Mutex` in `eframe`

* Expand clippy.toml files

* build fix

crates/epaint/src/text/text_layout_types.rs

@@ -1,4 +1,5 @@
 #![allow(clippy::derive_hash_xor_eq)] // We need to impl Hash for f32, but we don't implement Eq, which is fine
+#![allow(clippy::wrong_self_convention)] // We use `from_` to indicate conversion direction. It's non-diomatic, but makes sense in this context.
 
 use std::ops::Range;
 use std::sync::Arc;