Convert rustfmt from a submodule to a subtree

[jyn514]

r? @calebcartwright cc @Manishearth @Mark-Simulacrum

The motivation is that submodule updates cause rustfmt to not be available on nightly a lot; most recently it was unavailable for over 10 days, causing the beta release to be delayed. Additionally this is much less work on the part of the rustfmt maintainers to keep the rustfmt compiling, since now people making breaking changes will be responsible for fixing them.

I kept the rustfmt git history so it looks like there are thousands of commits. The important commits are https://github.com/rust-lang/rust/compare/851dee3af9404bf399c3c4ffefe5105edb3debad~..pull/82208/head. This adds about 10 MB of git history, which is not terribly much compared to the 702 MB that already exist.

• Add src/tools/rustfmt to x.py check

• Fix CRLF issues with rustfmt tests (see commit for details)

• Use rustc_private instead of crates.io dependencies

  This was already switched upstream and would have landed in the next submodule bump anyway. This just updates Cargo.lock for rust-lang/rust.

• Add yansi-term to the list of allowed dependencies.

  This is a false positive - rustc doesn't actually use it, only rustfmt, but because it's activated by the cargo feature of a dependency, tidy gets confused. It's fairly innocuous in any case, it's used for color printing.
  This would have happened in the next submodule bump.

• Remove rustfmt from the list of toolstate tools.

• Give a hard error if testing or building rustfmt fails.

• Update log to 0.4.14

  This avoids a warning about semicolons in macros; see the commit for details.

• Don't add tools to the sysroot when they finish building.

  This is the only change that could be considered a regression - this avoids a "colliding StableCrateId" error due to a bug in resolve (creader: Host crate loaded twice produces different CrateNums if host != target #56935). The regression is that this rebuilds dependencies more often than strictly necessary. See the commit for details.

Fixes #85226 (permanently). Closes #82385. Helps with #70651. Helps with #80639.

[Mark-Simulacrum]

Going to temporarily close this - it seems to be causing some trouble on bors, which is stalling out builds for other PRs. I will reopen and investigate in more detail tomorrow, but don't want to stall the queue overnight (for me).

[RalfJung]

Let's see if we can reopen now without harm. Also to be sure:
@bors r-

[RalfJung]

Can this be r+'d again? Looks like the merge conflict was resolved?

[Mark-Simulacrum]

We can try. @bors r+ rollup=never

[bors]

📌 Commit 34368ec has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 34368ec with merge eac3c7c...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing eac3c7c to master...