Rollup merge of #104483 - oli-obk:santa-clauses-make-goals, r=compiler-errors

Convert predicates into Predicate in the Obligation constructor

instead of having almost all callers do that.

This reduces a bit of boilerplate, and also paves the way for my work towards https://github.com/rust-lang/compiler-team/issues/531 (as it makes it easier to accept both goals and clauses where right now it only accepts predicates).