refact: win, virtual display (#7767)

* refact: win, virtual display

Signed-off-by: fufesou <shuanglongchen@yeah.net>

* Update flutter-build.yml

---------

Signed-off-by: fufesou <shuanglongchen@yeah.net>
Co-authored-by: RustDesk <71636191+rustdesk@users.noreply.github.com>

src/privacy_mode/win_topmost_window.rs

@@ -72,6 +72,10 @@ pub struct PrivacyModeImpl {
 }
 
 impl PrivacyMode for PrivacyModeImpl {
+    fn is_async_privacy_mode(&self) -> bool {
+        false
+    }
+
     fn init(&self) -> ResultType<()> {
         Ok(())
     }