The contents of this file have been moved in rust-lang#56932 (520e8b0) and the
file should have been removed as well.

…=matthewjasper

Refactorings to borrowck region diagnostic reporting

This PR is a followup to rust-lang#66886 and rust-lang#67404

EDIT: updated

In this PR:  Clean up how errors are collected from NLL: introduce `borrow_check::diagnostics::RegionErrors` to collect errors. This is later passed to `MirBorrowckCtx::report_region_errors` after the `MirBorrowckCtx` is created. This will allow us to refactor away some of the extra context structs floating around (but we don't do it in this PR).  `borrow_check::region_infer` is now mostly free of diagnostic generating code. The signatures of most of the functions in `region_infer` lose somewhere between 4 and 7 arguments :)

Left for future (feedback appreciated):

- Merge `ErrorRegionCtx` with `MirBorrowckCtx`, as suggested by @matthewjasper in rust-lang#66886 (comment)
- Maybe move the contents of `borrow_check::nll` into `borrow_check` and remove the `nll` submodule altogether.
- Find a way to make `borrow_check::diagnostics::region_errors` less of a strange appendage to `RegionInferenceContext`. I'm not really sure how to do this yet. Ideas welcome.

…asper

Misc MIR building cleanups

r? @matthewjasper

…-DPC

Remove iter_private.rs

The contents of this file have been moved in rust-lang#56932 (520e8b0) and the file should have been removed as well.