Auto merge of #136000 - matthiaskrgr:rollup-j6ge32r, r=matthiaskrgr

Rollup of 6 pull requests

Successful merges:

 - #135873 (coverage: Prepare for upcoming changes to counter creation)
 - #135926 (Implement `needs-subprocess` directive, and cleanup a bunch of tests to use `needs-{subprocess,threads}`)
 - #135950 (Tidy Python improvements)
 - #135956 (Make `Vec::pop_if` a bit more presentable)
 - #135966 ([AIX] Allow different sized load and store in `tests/assembly/powerpc64-struct-abi.rs`)
 - #135983 (Doc difference between extend and extend_from_slice)

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