In https://github.com/apple/swift/pull/65267 deserialization safety was made
more conservative, allowing deserialization of any protocol and
deserialization of any extension declaring an explicit conformance to any
protocol. We can refine this to only allow deserialization of safe protocols
and deserialization of extensions declaring conformances to safe protocols.
Importantly, though, we must look up all conformances declared by the
extension, not just the explicit ones.
Resolves rdar://114673761
Given a scenario where a public type A, conforms to an internal protocol
B, which conforms to a public protocol C. A conforms indirectly to C
through a protocol that's hidden from the clients.
This is handled in module interface by printing the indirect conformance
of A to C explicitly at the end of the swiftinterface.
We have the same problem with deserialization safety that used to hide
the internal protocols from clients, thus breaking the knowledge of the
indirect dependency. To keep the indirect conformances, let's consider
all protocols as safe and preserve their conformance information.
rdar://105241772
