app: set focused attribue on fore/background events for ios and android

[placid2000]

This path set focused flag in ConfigEvent when app goes back or foreground on ios and android

[eliasnaur]

In our discussion of this change, I wrote:

I now think the Config.Focused behaviour on Android is (subtly) wrong.
I'm thinking of Config.Focused as "the window has (keyboard) focus",
that is that the window is the one the user is currently interacting
with. In that sense, Config.Focused should probably change to match
the onPause/onResume lifecycle state on Android. The Java
OnFocusChangedListener should just be removed.
(With that change, it's possible the window.visible and started
states can be tracked in an lifecycle enum).

Why not use onPause/onResume and what about the focus listener?