[TIMOB-24598] Add Alloy attribute showAsDialog = true/false in Ti.UI.Picker on Android Titanium

It would be great if we can have a new Alloy XML property as *showAsDialog = true/false* on Ti.UI.Picker. In native Android, this property can be set on Spinner's XML attribute *android:spinnerMode* to *dialog or 0*. Having this property in Titanium will provide more UI options where many clients prefer to show a dialog instead of drop-down picker. Though we can create this dialog using Ti.UI.AlertDialog using androidView but it would disturb the parity in iOS & Android since setting only 1 property on Picker for Android will keep the parity & code same.