EMSUSD-1570 add a class-prims filter to USD UFE

[pierrebai-adsk]

• Add a getUsdPredicate helper function to UsdUfe to create the USD predicate corresponding to a list of UFE filters.
• Add the "Class Prims" filter to the list of USD filters in the hierarchy handler.
• Use the helper to create the USD predicate.
• Rely on the USD predicate having a correct predicate for inactive prim instead of using an explicit flag.
• Adjust the context menu for class prims.
• Add a unit test for the class prims filter.

Work around the problem that Maya does not correctly handle UFE filters. Maya only handles one UFE filter. If there are more than one filters, only one is handled.

To work around this issue, we manually ask the outliner what are the desired settings and use these settings as the default values for the filters. When the outliner fails to handle multiple filters, it will end-up using the default values, which will be the desired values.

[seando-adsk]

@pierrebai-adsk Removed the ready-for-merge just until my questions are answered.

[pierrebai-adsk]

I believe I answered Sean's concerns, so I'll mark this a ready for merge.