Feat/topmost window exclude from capture

[fufesou]

1. Check if windows version >= "Windows 2004", then use a better privacy mode implementation.
   https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setwindowdisplayaffinity
2. Remove redundent global variable CUR_PRIVACY_MODE_IMPL and PRIVACY_MODE_CONN_ID.
3. Send a "Exit privacy mode" message in the middle of swithing privacy mode.

windows-2004-1.mp4

windows-2004-2.mp4