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/shell/main.cpp

@@ -98,6 +98,7 @@ void display_usage() {
     std::cout << "  -pmmd:name  display Z3 module ('name') parameters in Markdown format.\n";
     std::cout << "  -pp:name    display Z3 parameter description, if 'name' is not provided, then all module names are listed.\n";
     std::cout << "  -tactics[:name]  display built-in tactics or if argument is given, display detailed information on tactic.\n";
+    std::cout << "  -simplifiers[:name]  display built-in simplifiers or if argument is given, display detailed information on simplifier.\n";
     std::cout << "  -probes     display avilable probes.\n";
     std::cout << "  --"      << "          all remaining arguments are assumed to be part of the input file name. This option allows Z3 to read files with strange names such as: -foo.smt2.\n";
     std::cout << "\nResources:\n";
@@ -295,6 +296,12 @@ static void parse_cmd_line_args(std::string& input_file, int argc, char ** argv)
                 else
                     help_tactic(opt_arg, false);
             }
+            else if (strcmp(opt_name, "simplifiers") == 0) {
+                if (!opt_arg)
+                    help_simplifiers();
+                else
+                    help_simplifier(opt_arg, false);
+            }
             else if (strcmp(opt_name, "tacticsmd") == 0 && opt_arg) 
                 help_tactic(opt_arg, true);
             else if (strcmp(opt_name, "probes") == 0)