Tracking issue for `const_patterns_without_partial_eq` lint

[RalfJung]

We used to (accidentally) accept some constants in patterns that don't even implement PartialEq. This is an accident and we'd like to hard-reject all such cases in the future. This lint catches those cases.

Relevant PRs:

• lint towards rejecting consts in patterns that do not implement PartialEq #115893: lint implementation