…r=BurntSushi

stabilize `Option::as_`(`mut_`)`slice`

This is the stabilization to rust-lang#108545. Thanks to everyone who helped getting this into Rust proper.

Add Span to various smir types

Had to make few extra changes to few structs to attach spans to them.

r? ``@oli-obk``

Move subtyper below reveal_all and change reveal_all

In previous attempt rust-lang#116378 we tried to handle `Opaque` in few different places, but this isn't necessary, after moving subtyper below reveal_all and calling `super_place` on reveal_all, issues cease to exist.

r? ``@oli-obk``

Fixes rust-lang#116332
Fixes rust-lang#116265
Fixes rust-lang#116383
Fixes rust-lang#116333

…cs, r=compiler-errors,estebank

Add a note to duplicate diagnostics

Helps explain why there may be a difference between manual testing and the test suite output and highlights them as something to potentially look into

For existing duplicate diagnostics I just blessed them other than a few files that had other `NOTE` annotations in

Do not assert that hidden types don't have erased regions.

cc rust-lang#116306

`args` can have erased regions.
In the linked issue, this is reached by computing whether a large type is `Freeze` to compute its ABI.

I do not have a minimized test to include.