And add a rustdoc-gui test confirming various header sizes.

…ldn't

using "b" and "d" can be easily confused

Add a couple tests for normalize under binder issues

Closes rust-lang#56556
Closes rust-lang#76956

r? `@nikomatsakis`

enable `i8mm` target feature on aarch64 and arm

As in rust-lang/stdarch#1233, `i8mm` needs to be turned on to support the implementation of `vmmla` and `vusmmla`neon instructions in stdarch.
r? `@Amanieu`

…omez

Fix documentation header sizes

And add a rustdoc-gui test confirming various header sizes.

Split off from rust-lang#90156. This fixes a regression in rust-lang#89506 where the heading level of titles within Markdown was too high (h2) for docblocks under structs, unions, and enum impls.

r? `@camelid`

Demo: https://jacob.hoffman-andrews.com/rust/fix-header-sizes/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E
Stable: https://doc.rust-lang.org/stable/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E
Beta: https://doc.rust-lang.org/beta/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E

…camelid

Tooltip overflow

Fixes rust-lang#89185.

r? `@camelid`

Changed slice.swap documentation for better readability

The example exchanges the letters "b" and "d", these can be easily confused and are hard to read for people with dyslexia.
Therefore, I changed the example to a more easily readable one.

This is just a small fix and it's not urgent by any means, but I spent 5 minutes trying to understand why I couldn't see any change so I fixed it.

Anyway, thank you for all your works!