RESTRICT AUTOMERGE - Allow ResolverActivity to relinquish task identity

Or the task effective uid may still be system uid after
ResolverActivity finishes.

The ResolverActivity should relinquish the task identity
to the next activity, just like ChooserActivity does.

Bug: 205996115
Test: manually check the task effective uid of the test app
Change-Id: I311da4e7fe9fd715f29202c0882891ec1d9dd1d2