Update of unused.rb

[paulmaxgithub]

It was added:

1. "CodingKeys" to ignore enum (CodingKeys: String, CodingKey)
2. "@main" to ignore all entry point files, such as AppDelegate or application type in SwiftUI implementation
3. "Previews" to ignore all PreviewProvider type structures that present user interfaces in SwiftUI interfaces
4. |typealias| to find unused typealias in code