Make AndroidPackage.(requested|implicit)Permissions a Set.

It is often checked for contains(), and for packages that request 300+
permissions the difference between binary search and linear search may
be significant. On the other hand, iterating over an ArraySet via
iterator isn't super slow either - mostly just one more allocation for
the iterator and should be worth the trade-off.

Bug: 284205103
Test: presubmit
Change-Id: I525f5ec8efb0ec402a8cde3e64fd66dea4b20277