Fix clang warnings about casting away const. (#9933)

This is another PR towards the goal of getting Z3 to compile cleanly
when included via FetchContents into clang-tidy, which uses a pretty
strict set of warnings.

This PR adds
```
"-Wcast-qual"
```
to the set of warnings enabled in the build.  This gives warnings like:
```
/Users/daviddetlefs/z3/src/ast/ast.cpp:2897:38: warning: cast from 'app *const *' to 'expr **' drops const qualifier [-Wcast-qual]
```
I fixed these by inserting consts. In some cases, a "const_cast<T>(...)"
was necessary.

src/api/z3_replayer.cpp

@@ -621,7 +621,7 @@ struct z3_replayer::imp {
 
     Z3_symbol get_symbol(unsigned pos) const {
         check_arg(pos, SYMBOL);
-        return (Z3_symbol)m_args[pos].m_sym;
+        return (Z3_symbol)const_cast<void*>(m_args[pos].m_sym);
     }
 
     void * get_obj(unsigned pos) const {