iOS: always attach picker menu to a cleared focus object

Change-Id: I32ad628e2fcdce43cf85ff9d2128187bca46ee40
iOS: implement QIOSInputContext::isAnimating()

Change-Id: I13f6c647ec0c820c4f207eee091651c73ce5747c
iOS: change QIOSInputContext::isVisible() to follow documentation

The documentation states that visible should be true from the moment
the keyboard start animating into becoming fully visible.

Change-Id: I393d36330df6c3b9fb703b3e2d9c297a4d59daf9