- Removes `native_menu.h` dependency from `display_server.h`.
It's now forward-declared in all DisplayServer implementations and should
be included in the .cpp's.
- Removes some unused `rb_set.h` and `rb_map.h` dependencies, which leads to
having to include them explicitly in half the scene and editor codebase...
which shows how much we depend on `display_server.h`.
- Forward-declare `input_event.h`, so now we need only `keyboard.h`.
- Introduces a SCons builder for Swift files
- Increases the minimum deployment targets to iOS 14.0, and visionOS 26.0.
- Replaces manually UIWindow management by a SwiftUI instantiated app.
