AST: Add some assertions to PackType::get()
AST: Add some assertions to PackType::get()

roambotics/swift,roambotics/swift,apple/swift,apple/swift,apple/swift,apple/swift,roambotics/swift,roambotics/swift,glessard/swift,apple/swift,glessard/swift,glessard/swift,glessard/swift,roambotics/swift,apple/swift,glessard/swift,roambotics/swift,glessard/swift