fix: declare a quantifier's decl rather than itself in SMT translation

This fixes an issue where malformed SMT problems would be produced from
expressions within quantified sections. The quantified variable would be
declared using the ID of the quantifier, but then references to it would use the
ID of the quantifier's contained declaration. As a result, SMT solvers would
reject the problem for referring to an undeclared variable.

This bug was actually identified while trying to implement forall support in the
SMT bridge. The upcoming tests for this provoke the bug.