Check for array lengths that aren't actually `usize`

I wish typeck wouldn't give us `ty::Array`s that have this problem in the first place, but we can check for it.

Fixes rust-lang#134352
cc `@matthiaskrgr`

…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#134202 (Remove `rustc::existing_doc_keyword` lint)
 - rust-lang#134354 (Handle fndef rendering together with signature rendering)
 - rust-lang#134368 (Use links to edition guide for edition migrations)
 - rust-lang#134371 (Check for array lengths that aren't actually `usize`)
 - rust-lang#134378 (An octuple of polonius fact generation cleanups)

Failed merges:

 - rust-lang#134365 (Rename `rustc_mir_build::build` to `builder`)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#134202 (Remove `rustc::existing_doc_keyword` lint)
 - rust-lang#134354 (Handle fndef rendering together with signature rendering)
 - rust-lang#134368 (Use links to edition guide for edition migrations)
 - rust-lang#134371 (Check for array lengths that aren't actually `usize`)
 - rust-lang#134378 (An octuple of polonius fact generation cleanups)

Failed merges:

 - rust-lang#134365 (Rename `rustc_mir_build::build` to `builder`)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#134202 (Remove `rustc::existing_doc_keyword` lint)
 - rust-lang#134354 (Handle fndef rendering together with signature rendering)
 - rust-lang#134368 (Use links to edition guide for edition migrations)
 - rust-lang#134371 (Check for array lengths that aren't actually `usize`)
 - rust-lang#134378 (An octuple of polonius fact generation cleanups)

Failed merges:

 - rust-lang#134365 (Rename `rustc_mir_build::build` to `builder`)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#134124 (CI: use free runners for x86_64-gnu-llvm jobs)
 - rust-lang#134197 (rustc_mir_build: Clarify that 'mirrored' does not mean 'flipped' or 'reversed')
 - rust-lang#134260 (Correctly handle comments in attributes in doctests source code)
 - rust-lang#134277 (rustdoc-search: handle `impl Into<X>` better)
 - rust-lang#134284 (Keep track of patterns that could have introduced a binding, but didn't)
 - rust-lang#134337 (reject unsound toggling of RISCV target features)
 - rust-lang#134371 (Check for array lengths that aren't actually `usize`)
 - rust-lang#134385 (tests/ui/asm: Remove uses of rustc_attrs, lang_items, and decl_macro features by using minicore)
 - rust-lang#134386 (Some trait method vs impl method signature difference diagnostic cleanups)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#134371 - scottmcm:fix-134352, r=oli-obk

Check for array lengths that aren't actually `usize`

I wish typeck wouldn't give us `ty::Array`s that have this problem in the first place, but we can check for it.

Fixes rust-lang#134352
cc ``@matthiaskrgr``

…-obk"

This reverts commit 7c301ec, reversing
changes made to dffaad8.

Temporarily bring back `Rvalue::Len`

r? `@compiler-errors` as requested in rust-lang#135671 (comment)

> However, in the mean time, I'd rather we not crunch trying to find and more importantly validate the soundness of a solution 🤔

Agreed. To fix the IMO P-critical rust-lang#135671 for which we somehow didn't have test coverage, this PR temporarily reverts:
- rust-lang#133734
- its bugfix rust-lang#134371
- rust-lang#134330

cc `@scottmcm`

I added the few samples from that issue as a test, but we can add more in the future, in particular it seems `@steffahn` [will work on that](rust-lang#135671 (comment)).

Fixes rust-lang#135671. And if we want to land this, it should also be nominated for beta backport.