Add simplification customization for SMTLIB2

Add the ability to customize incremental pre-processing simplification for the SMTLIB2 front-end. The main new capability is to use pre-processing tactics in incremental mode that were previously not available. The main new capabilities are
- solve-eqs
- reduce-args
- elim-unconstrained
There are several more. Documentation and exposed simplifiers are populated incrementally. The current set of supported simplifiers can be inspected by using z3 with the --simplifiers flag or referring to https://microsoft.github.io/z3guide/docs/strategies/simplifiers

Some pending features are:
- add the ability to update parameters to simplifiers similar to how tactics can be controlled using parameters.
- expose simplification solvers over the binary API.

src/ast/simplifiers/bit_blaster.h

@@ -49,3 +49,6 @@ public:
 
 };
 
+/*
+  ADD_SIMPLIFIER("bit-blaster", "reduce bit-vector expressions into SAT.", "[](auto& m, auto& p, auto &s) -> dependent_expr_simplifier* { return alloc(bit_blaster_simplifier, m, p, s); }")
+*/