Do not load xml metadata for unchanged packages in RegisteredServicesCache

RegisteredServicesCache caches services in an xml, so the system doesn't
have to scan all the apks. Whenever a package is changed
(add/remove/replaced), the broadcast receiver in RegisteredServicesCache
will refresh this cache by quering all matching services and reading their
xml metadata. There is extra work done here, because only the changed package
will have services added/removed.

This change changes RegisteredServicesCache to only get the service info of changed packages.

Bug: 117755076
Test: atest RegisteredServicesCache
Change-Id: I2d9e7980fcd651617e450ff12e1588601de4ef6c