Only add widgets system shortcut if widgets exist

Before we were adding it in a disabled state, and then enabling it once
widgets were bound (if widgets existed for that app). Now we load all
widgets when launcher starts so that we can use the values for the
purpose of animating the popup container. Then, as the container opens,
we reload widgets/shortcuts for that particular app and add/remove the
widgets shortcut if necessary.

Bug: 34940468
Change-Id: I64bd009442d10d3d1f9a977bdedfdb639a7dd193