Chooser filtering and caller direct share targets

Let apps invoking the system chooser specify components to filter out
such as themselves; this will prevent duplicate nonsensical UX where
it doesn't make sense for an app to share to itself.

Similarly, let apps provide their own Direct Share targets for when
they do want to let users share via their own internal services in the
same UI. These options can be used together.

Also fix a bug where a lingering binder reference from a remote
ChooserTargetService that hasn't been GC'd in the remote process could
keep an active reference to a ChooserActivity instance.

Bug 28073484

Change-Id: Ib613b1153b49dfedf79574b1af7c45379eceec24