Reorder Ember.View#_toggleVisibility

Previously, this function was a no-op if the view's element was not
in the DOM. That meant that if such a view's `isVisible` property
changed, `_toggleVisibility` wouldn't make it far enough to sync up
its internal `_isVisible` property with the new `isVisible` value.

With those two values out of sync, if the view's `isVisible` changed
*again*, `_isVisibleDidChange` wouldn't properly schedule (or
properly *not* schedule) a subsequent call to `_toggleVisibility`.
Thus, the view's actual DOM visibility would no longer match its
`isVisible` property.

Closes #5329