This is a very small win.

Fixes rust-lang#70856

This was a relic from when we had "nominal flags" and "cached
properties." The latter no longer exists, so nominal flags are no
longer necessary. In fact, every flag is considered a nominal flag. I
went ahead and removed all references to NOMINAL_FLAGS.

Fixes rust-lang#70836

remove false positives of unused_braces

fixes rust-lang#70717

We could potentially be more aggressive when linting let bindings by checking if there are any explicit `ref`s.
I have been unable to create a snippet which compiles when using braces but has a borrowck error
without them. The closes I've gotten is [the following (playground)](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=4a1552ebe9648cb13fcb8dd969189a6c).

r? @eddyb

…Mark-Simulacrum

ci: move /var/lib/docker to /mnt on GHA

There are some builders that are running out of disk space while building the Docker images, such as arm-android. This moves and symlinks `/var/lib/docker` to the `/mnt` partition on Linux GHA.

Example of a build failing because of this: https://github.com/rust-lang-ci/rust/runs/564628621

BTreeMap first last proposal tweaks

Clean-up and following up on a request in rust-lang#62924.

Trying the reviewer of the original code rust-lang#65637...
r? @scottmcm

…r=estebank

Use a `SmallVec` for `Cache::predecessors`.

This is a very small win.

…an-DPC

Clean up E0507 explanation

r? @Dylan-DPC

…sakis

wf: refactor `compute_trait_ref`

moves `extend_cause_with_original_assoc_item_obligation` out of `compute_trait_ref` and
changes `trait_assoc_items` to an iterator. This saves us from building an unnecessary `Vec<_>`

r? @eddyb i guess

Corrects a typo in rustdoc documentation.

Fixes rust-lang#70856

Sorry, I am just learning git and I think I may have accidentally done some wacky stuff that closed my last PR. Here it is again.

Remove unnecessary TypeFlags::NOMINAL_FLAGS

This was a relic from when we had "nominal flags" and "cached
properties." The latter no longer exists, so nominal flags are no
longer necessary. In fact, every flag is considered a nominal flag. I
went ahead and removed all references to NOMINAL_FLAGS.

Fixes rust-lang#70836

…an-DPC

Clean up E0510 explanation

r? @Dylan-DPC