Auto merge of #108121 - aliemjay:resolve-var-region, r=lcnr

always resolve to universal regions if possible

`RegionConstraintCollector::opportunistic_resolve_var`, which is used in canonicalization and projection logic, doesn't resolve the region var to an equal universal region. So if we have equated `'static == '1 == '2`, it doesn't resolve `'1` or `'2` to `'static`. Now it does!

Addresses review comment rust-lang/rust#107376 (comment).

r? `@lcnr`