swift

620462dd - Sema: Don't diagnose declarations more available than unavailable container.

Sema: Don't diagnose declarations more available than unavailable container. It turns out that we must allow declarations with `introduced:` availability nested inside of other declarations that are `unavailable` in order to influence weak linking. Stop diagnosing declarations as being more available than their unavailable containers and revert some changes to availability inference that were designed to avoid creating these nestings but caused regressions for declarations marked `@_spi_available.` Reverts parts of https://github.com/apple/swift/pull/64310, https://github.com/apple/swift/pull/64015, and https://github.com/apple/swift/pull/62900.