Auto merge of #130249 - compiler-errors:sad-new-solver-coherence, r=lcnr

Revert "Stabilize `-Znext-solver=coherence`"

This is a clean revert of #121848, prepared by running:

```
$ git revert 17b322fa69eed7216dccc9f097eb68237cf62234 -m1
```

Which effectively reverts:
* a138a9261536ac2bdbb7c01a8aa9dc7d43299cae, 69fdd1457d367ce4de044e9784e58a38acf3d847, d93e047c9f1b33892a604273ab3931815f5604a1, 1a893ac648e03732aaa8b5371b602ab683970b0d

see: https://rust-lang.zulipchat.com/#narrow/stream/364551-t-types.2Ftrait-system-refactor/topic/nalgebra.20hang

Closes #130056

r? lcnr