When normalizing a projection which results in a cycle, we would
cache the result of `project_type` without the nested obligations
(because they're not needed for inference). This would result in
the nested obligations only being handled once in fulfill, which
would avoid the cycle error.
Fixes#79714, a regresion from #79305 caused by the removal of
`get_paranoid_cache_value_obligation`.
Only check the own predicates of associated types when confirming
projection candidates.
Also consider implied bounds when comparing trait and impl methods.
Normalizing `<dyn Iterator<Item = ()> as Iterator>::Item` no longer
requires selecting `dyn Iterator<Item = ()>: Iterator`. This was
previously worked around by using a special type-folder to normalize
things.
