add removeKeyEvents()

[q-depot]

when you open a file dialog(open/save) the main app window looses the focus without calling keyUp. The key down events are not released and imgui sliders and scroll don't work anymore, you can see the issue from the imgui test window in the "keyboard, mouse & focus" tab. removeKeyEvents() can be called after the file dialog is opened to reset all ImGui key events to false.