API change for cross profile calendar feature.

According to new requirements in b/121179845, we are changing the
API pattern from "add/remove" to "set(set<string>)" to support
"enable all packages" operation. Setting the whitelist to null
will enable all packages. This behavior is consistent with existing
methods in DevicePolicyManager, e.g. setPermittedInputMethods.

Also corrected some languages in the comments and annotations.

Bug: 121179845
Test: atest ManagedProfileTest#testCrossProfileCalendar
atest DevicePolicyManagerTest

Change-Id: I87f17a2094792e44fdeb672658bddb871c2c1eeb