Implement basic operations for rule XML parsing

XML rule parsing would extract rules from strings or input streams. XML
format should match the rule format defined in the integrity model. This
change adds basic rule extraction with basic validation.

Bug: 143697198
Test: atest FrameworksServicesTests:RuleXmlParserTest
Change-Id: I3deff06be086a77238a43b1488c6e3f4ca03c585