Update bitflags to 2.0

Co-authored-by: dAxpeDDa <daxpedda@gmail.com>

src/platform_impl/macos/appkit/window.rs

@@ -336,6 +336,7 @@ unsafe impl Encode for NSWindowLevel {
 }
 
 bitflags! {
+    #[derive(Clone, Copy)]
     pub struct NSWindowOcclusionState: NSUInteger {
         const NSWindowOcclusionStateVisible = 1 << 1;
     }
@@ -346,6 +347,7 @@ unsafe impl Encode for NSWindowOcclusionState {
 }
 
 bitflags! {
+    #[derive(Debug, Clone, Copy)]
     pub struct NSWindowStyleMask: NSUInteger {
         const NSBorderlessWindowMask      = 0;
         const NSTitledWindowMask          = 1 << 0;