Move quantifiers engine private to own file (#5053)

Move quantifiers engine private to own file (#5053)

This moves and renames the quantifiers engine private class to QuantifiersModules. This is in preparation for using a standard state and inference manager object in TheoryQuantifiers and QuantifiersEngine.

Initializing quantifiers engine is a bit non-standard since it is intentionally a separate entity from TheoryQuantifiers. However, the plan is for quantifiers engine to use the state and inference manager of TheoryQuantifiers.

This PR additionally moves the initialization of quantifiers modules to a QuantifiersEngine::finishInit() method. The motivation for is that we do not have a state and inference manager during construction of QuantifiersEngine, since these will live in TheoryQuantifiers and will be passed to QuantifiersEngine during TheoryQuantifiers::finishInit. This means that we need a final pass to initialize quantifiers engine after these are initialized, which thus must come as the last step of TheoryEngine::finishInit.

The next PR will connect the state and inference manager to QuantifiersEngine during TheoryQuantifiers::finishInit. Then, the plan is for many of the core utilities in QuantifiersEngine to migrate to state/inference manager, and finally for its modules to reference state and inference manager instead of QuantifiersEngine.