Auto merge of #118970 - aliemjay:rollup-or33al2, r=aliemjay

Rollup of 2 pull requests

Successful merges:

 - #118927 (Erase late bound regions from `Instance::fn_sig()` and add a few more details to StableMIR APIs)
 - #118964 (Opportunistically resolve region var in canonicalizer (instead of resolving root var))

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