Enable local search for instant apps

When getting the set of searchable activities, fetch instant
applications. But, this means that the set needs a final
filter to prevent leaking application existence.

Change-Id: I6b9daf031ce54061c4500d9edae1d738848158c4
Fixes: 68211791
Test: atest -it CtsAppSecurityHostTestCases:EphemeralTest#testGetSearchableInfo