Rollup merge of #82007 - sexxi-goose:reborrow, r=nikomatsakis

Rollup merge of #82007 - sexxi-goose:reborrow, r=nikomatsakis

Implement reborrow for closure captures

The strategy for captures is detailed here with examples: https://hackmd.io/PzxYMPY4RF-B9iH9uj9GTA

Key points:
- We only need to reborrow a capture in case of move closures.
  - If we mutate something via a `&mut` we store it as a `MutBorrow`/`UniqueMuBorrow` of the path containing the `&mut`,
  - Similarly, if it's read via `&` ref we just store it as a `ImmBorrow` of the path containing the `&` ref.
  - If a path doesn't deref a `&mut`, `&`, then that path is captured by Move.
  - If the use of a path results in a move when the closure is called, then that path is truncated before any deref and the truncated path is moved into the closure.

- In the case of non-move closure if a use of a path results in a move, then the path is truncated before any deref and the truncated path is moved into the closure.

Note that the implementation differs a bit from the document to allow for truncated path to be used in the ClosureKind analysis that happens as part of the first capture analysis pass.

Closes: https://github.com/rust-lang/project-rfc-2229/issues/31
r? ````@nikomatsakis````