This commit updates the `darwin/Foundation` package's `NSScreen` bindings
to treat Objective-C "type properties" as class methods rather than
instance methods.
As a result, we can now access these properties like this:
```odin
import NS "core:sys/darwin/Foundation"
main :: proc() {
NS.Screen.mainScreen()
}
```
instead of this:
```odin
import NS "core:sys/darwin/Foundation"
main :: proc() {
(^NS.Screen)(nil).mainScreen()
}
```
This commit also adds a binding for `NSScreen`'s `screensHaveSeparateSpaces`
type property, which was previously missing from the `darwin/Foundation`
package.
Co-authored-by: Jacob Evelyn <j@cob.land>
