Fix array_exprt handling in incremental SMT2 procedure

The call to `define_dependent_functions` ensures that `array_exprt`
expressions are properly handled and their dependent functions are
defined before the expression conversion process begins.

Fixes: #8080

Author: tautschnig

regression/cbmc/array-cell-sensitivity12/test_execution.desc

@@ -1,4 +1,4 @@
-CORE no-new-smt
+CORE
 test.c
 
 ^VERIFICATION FAILED$

src/solvers/smt2_incremental/smt2_incremental_decision_procedure.cpp

@@ -377,6 +377,7 @@ smt_termt
 smt2_incremental_decision_proceduret::convert_expr_to_smt(const exprt &expr)
 {
   define_index_identifiers(expr);
+  define_dependent_functions(expr);
   const exprt substituted = substitute_defined_padding(
     substitute_identifiers(expr, expression_identifiers));
   track_expression_objects(substituted, ns, object_map);