Generate license html file from xml files of partitions

Treble-ization requires each partner to store their license information
into their own partition because each partition can be updated
individually.
So each partition will have its own NOTICE.xml.gz, and Settings should
be able to generate license html from xml files of partitions.

Test: building succeeded and tested on sailfish.
  make ROBOTEST_FILTER=LicenseHtmlGeneratorFromXmlTest RunSettingsRoboTests
  make ROBOTEST_FILTER=LicenseHtmlLoaderTest RunSettingsRoboTests
  make ROBOTEST_FILTER=SettingsLicenseActivityTest RunSettingsRoboTests
Bug: 37099941
Change-Id: If797759d300ee20dd43ad8efd7d17b4f7e0c4537