add clausal lookahead to arithmetic solver as part of portfolio

have legacy qfbv-sls solver use nnf pre-processing. It relies on it for correctness of the score updates.

src/ast/sls/CMakeLists.txt

@@ -3,6 +3,7 @@ z3_add_component(ast_sls
     bvsls_opt_engine.cpp
     sat_ddfw.cpp
     sls_arith_base.cpp
+    sls_arith_clausal.cpp
     sls_arith_plugin.cpp
     sls_array_plugin.cpp
     sls_basic_plugin.cpp