Support Swift 5.8 and part of 5.9

• Add keywords for conditional compilation and annotations.
  • hasFeature
    https://github.com/apple/swift-evolution/blob/main/proposals/0362-piecemeal-future-features.md
  • hasAttribute
    https://github.com/apple/swift-evolution/blob/main/proposals/0367-conditional-attributes.md
  • before
    https://github.com/apple/swift-evolution/blob/main/proposals/0376-function-back-deployment.md
  • Various environment names
• if expresison and switch expression (Swift 5.9).
  https://github.com/apple/swift-evolution/blob/main/proposals/0380-if-switch-expressions.md
• Bug fixes and CI improvements.