Bug fix + clean up on component alias

- The "overrides" device config was supposed to use "," as a separator,
  but accidentally using "+" instead.

- Improved BroadcastMessenger.

- ComponentAliasResolver.Resolution now is a generic class.
  I'm using it with String for provider authority aliases.

Bug: 197264681
Test: atest ComponentAliasServiceTest
Change-Id: Iaa8f4e67bfd8cae93755f68d821da0ba9f48dd41