Auto merge of rust-lang#142544 - Sa4dUs:prevent-abi-changes, r=ZuseZ4

Prevent ABI changes affect EnzymeAD

This PR handles ABI changes for autodiff input arguments to improve Enzyme compatibility. Fundamentally this adjusts activities when a function argument is lowered as an `ScalarPair`, so there's no mismatch between diff activities and args. Also removes activities corresponding to ZSTs.

fixes: rust-lang#144025

r? `@ZuseZ4`

Author: bors