Change ComponentReference "hasFeature" to "refersTo"

[tcmitchell]

See SynBioDex/SBOL-specification#461 for the origin story.

This change in the specification will require updates to the following SBOL3 test files:

• combine2020
• multicellular
• toggle_switch
• multicellular_simple

[tcmitchell]

I'm pinging on this now that @jakebeal has closed SynBioDex/SBOL-specification#461 and the 3.0.1 specification seems headed towards completion. This issue is preventing pySBOL3 from implementing this change. See SynBioDex/pySBOL3#276

@goksel do you think this is hard to fix? Does libSBOLj3 already implement "refersTo"?

[goksel]

I updated the TestSuite files with the new ComponentReference.refersTo property.