Auto merge of #119849 - lcnr:eagerly-instantiate-binders, r=compiler-errors

more eagerly instantiate binders

The old solver sometimes incorrectly used `sub`, change it to explicitly instantiate binders and use `eq` instead. While doing so I also moved the instantiation before the normalize calls. This caused some observable changes, will explain these inline. This PR therefore requires a crater run and an FCP.

r? types

Author: bors