Re-use existing app even for non-multi-instance apps

* Previously we only restarted previous tasks if
the app being dragged/started was of the same package as
the existing/other side's package
* Now we always attempt to restart a previous task that
has the same component/userId key

Fixes: 296151858
Test: Existing tests pass, modified unit test to verify
package/multi-instance checks don't get run since previous
task restarting isn't dependent on that anymore.
Manually tested with dragging multi (Sheets, Chrome) + non-multi
instance apps and things seemed fine.

Change-Id: Ie3c1dae8966341eaa520cec1af720bce5be55c62