Rollup merge of #138528 - dianne:implicit-deref-patterns, r=Nadrieril

deref patterns: implement implicit deref patterns

This implements implicit deref patterns (per https://hackmd.io/4qDDMcvyQ-GDB089IPcHGg#Implicit-deref-patterns) and adds tests and an unstable book chapter.

Best reviewed commit-by-commit. Overall there's a lot of additions, but a lot of that is tests, documentation, and simple(?) refactoring.

Tracking issue: #87121

r? ``@Nadrieril``

Author: matthiaskrgr