The method RootView:on_mouse_pressed was copied in the contextmenu plugin with
a small modification to intercept the mouse clicks of the active view.
This approach is problematic because a relatively large portion of code is
duplicated.
We introduced a function named RootView.on_view_mouse_pressed to let plugins
like contextmenu intercepts mouse clicks in the active area without duplicating
the function RootView:on_mouse_pressed.