Ensure the active window gains the keyboard focus

[garychia]

Fixes #80470
The issue occurred when another window was about to minimize, the currently active window would become inactive temporarily and lose the keyboard focus, and then become active again after the minimizing was complete. However, the active window would not regain the keyboard focus automatically so it would not receive any WM_CHAR message.

My solution is based on this documentation. It mentions the DefWindowProc function sets the keyboard focus to the window being activated and not minimized. This mechanism is not found in the current implementation of DisplayServerWindows::WndProc function.

[groud]

cc @RandomShaper

[RandomShaper]

Why is IsIconic() needed?

[garychia]

IsIconic() is used to ensure any minimized window being activated does not gain the keyboard focus. According to the remarks section of this page, what I understand is that a window can be activated when it is minimized and allowing a minimized window to gain the keyboard focus may not be an expected behavior.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.2.2.