Smtml.RewriteSourceModule that performs two 'important' rewritings:
1. Replace symbols' Ty_none with the correct type specified in declare-const.
2. Propagate the correct theory encoding for Unop, Binop, Relop, and Triop.
3. Inlines Let_in binders into a single big expr
module Symb_map : sig ... endPropagates types in type_map and inlines Let_in binders
Acccumulates types of symbols in type_map and calls rewrite_expr