Auto merge of #85868 - Aaron1011:projection-cache, r=jackh726

Preserve most sub-obligations in the projection cache

Fixes https://github.com/rust-lang/rust/issues/85360

When we evaluate a projection predicate, we may produce sub-obligations. During trait evaluation, evaluating these sub-obligations might cause us to produce `EvaluatedToOkModuloRegions`.

When we cache the result of projection in our projection cache, we try to throw away some of the sub-obligations, so that we don't need to re-evaluate/process them the next time we need to perform this particular projection. However, we may end up throwing away predicates that will (recursively) evaluate to `EvaluatedToOkModuloRegions`. If we do, then the result of evaluating a predicate will depend on the state of the predicate cache - this is global untracked state, which interacts badly with incremental compilation.

To fix this, we now only discard global predicates that evaluate to `EvaluatedToOk`. This ensures that any predicates that (may) evaluate to `EvaluatedToOkModuloRegions` are kept in the cache, and influence the results of any queries which perform this projection.

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