macOS: add WindowEvent::PointerButton::is_macos_activation_click

Apps need per-click decisions to follow the macOS convention of accepting
first mouse for low-risk actions (selection, scrolling) but rejecting it
for buttons and destructive actions. Motivated by slint-ui/slint#10451.

Always return `true` from `acceptsFirstMouse:`, and tag the resulting
`PointerButton` events with `is_macos_activation_click: true` (on both
the activating left press and its matching release) so the app can
short-circuit the whole gesture with a single check:

    WindowEvent::PointerButton { is_macos_activation_click: true, .. } => return,

Replaces an earlier callback-based design (`accepts_first_mouse` on
`ApplicationHandlerExtMacOS`) that mapped more closely to AppKit but
didn't fit winit's event-driven model and required re-entrancy handling.

Also removes `WindowAttributesMacOS::with_accepts_first_mouse`, which is
now redundant — apps that want to reject activation clicks check the
flag on the per-event instead.

winit-wayland/src/seat/pointer/mod.rs

@@ -187,6 +187,7 @@ impl PointerHandler for WinitState {
                             state,
                             position,
                             button,
+                            is_macos_activation_click: false,
                         },
                         window_id,
                     );

winit-wayland/src/seat/touch/mod.rs

@@ -67,6 +67,7 @@ impl TouchHandler for WinitState {
                 state: ElementState::Pressed,
                 position,
                 button: ButtonSource::Touch { finger_id, force: None },
+                is_macos_activation_click: false,
             },
             window_id,
         );
@@ -120,6 +121,7 @@ impl TouchHandler for WinitState {
                 state: ElementState::Released,
                 position,
                 button: ButtonSource::Touch { finger_id, force: None },
+                is_macos_activation_click: false,
             },
             window_id,
         );

winit-wayland/src/types/wp_tablet_input_v2.rs

@@ -235,6 +235,7 @@ impl Dispatch2<ZwpTabletToolV2, WinitState> for TabletToolData {
                                     button,
                                     data: data.tool_state.clone(),
                                 },
+                                is_macos_activation_click: false,
                             }
                         },
                         TabletEvent::Left => WindowEvent::PointerLeft {