Extended array theories support for Princess and Eldarica

[sankalpgambhir]

Major:

• Add support for Princess extensional arrays, and by extension sets
• the Princess solver now supports Maps, Sets, and Bags (WIP)
• Set support for SMTLIB solvers is factored into a separate file, and this support is extended to Eldarica

Minor:

• Change z3 subset check to use the more standard (_ map =>), which now allows using sets with Spacer as well

Issues:

• currently needs princess and eldarica nightlies
• Semantics suite for sets on Princess fails on some set tests due to simplifier issues that happen before even getting to princess, which I haven't yet managed to understand