Provide inheritance in SolarSystemLib tests

Summary:
To correctly test is_a / instanceof equivalent bevhavior in reflection code,
provide interface and base class to SolarSystemLib test library.

Ref T2308

Test Plan:

• Test for full library load updated to include new objects
• No feature has been added, this is no-op

Maniphest Tasks: T2308

Differential Revision: https://devcentral.nasqueron.org/D4064