swift

85b66d1d - [ConformanceLookup] Always prefer unavailable Sendable conformances from the

[ConformanceLookup] Always prefer unavailable Sendable conformances from the defining module, and diagnose redundant Sendable conformances. We still allow re-stating inherited unchecked Sendable conformances in subclasses because inherited Sendable conformances are surprising when they opt out of static checking. Otherwise, warning on redundant Sendable conformances nudges programmers toward cleaning up unnecessary retroactive Sendable conformances over time as libraries incrementally add the conformances directly.