Collect Uri grants for startActivities().

It looks like the implementation of startActivities() was resolving
the target ActivityInfo, but it wasn't collecting the needed Uri
permission grants.

This change updates startActivities() to use the same logic used by
ActivityStarter.Request.resolverActivity(), where we collect the
grants immediately after ActivityStackSupervisor.resolveActivity().

Bug: 159412574
Test: atest CtsAppSecurityHostTestCases:android.appsecurity.cts.AppSecurityTests#testPermissionDiffCert
Change-Id: I4e92701b7b9bb23307a4eeca27d33b78537c2805