Add testBuild API to ARS and clean up flag querying

[stonar96]

• Add testBuild API to ARS
• Add interface(s) with common methods of ARS and FlagValueCalculator
• Clean up lots of stuff related to the flag querying methods
• Remove much duplicated code and docs by using the new interface(s)
• Deprecate some unnecessary overloads for removal in WG 8
• Fix PermissiveRegionSet returning DENY for the build flag

When the deprecated methods are removed, ARS (and subclasses), FlagValueCalculator and RegionQuery now have completely consistent methods for querying flags with the least code and docs duplication. Especially the docs of the different versions of the "same" methods have desynced over time a bit. The methods are now defined and documented in a central place (the interfaces). The convenience methods of RegionQuery now purely delegate to ARS, so I've removed their docs too and linked to ARS.