app: [API] add minimized window mode, change methods to options

The window modes are extended, following microsoft conventions.
We have Fullscreen, Overlapping, Maximized and Minimized.
These modes can be set via options when a new window is creates,
or modified later by calling helper functions like w.Maximize() and w.Center()

The window configuration is automatically updated when a user
modifies the window by dragging or clicking the icons on the window's title-bar,
minimizing or maximizing the window.

Any change, either by the user or the application will emit a ConfigChange event.

This is implemented and tested on Windows only.

API change. the app.Window methods Maximize and Center are replaced with similar
options. For example, to maximize a window use

    w.Option(app.Maximized.Option())

Also, Maximize and Center implementations for X11 and macOS are left for a future
change.

Fixes: https://todo.sr.ht/~eliasnaur/gio/315
Signed-off-by: Jan Kåre Vatne <jkvatne@online.no>

app/os_android.go

@@ -1261,12 +1261,6 @@ func setNavigationColor(env *C.JNIEnv, view C.jobject, color color.NRGBA) {
 // Close the window. Not implemented for Android.
 func (w *window) Close() {}
 
-// Maximize maximizes the window. Not implemented for Android.
-func (w *window) Maximize() {}
-
-// Center the window. Not implemented for Android.
-func (w *window) Center() {}
-
 // runOnMain runs a function on the Java main thread.
 func runOnMain(f func(env *C.JNIEnv)) {
 	go func() {