[LLDB][formatters] ArgInfo::count -> ArgInfo::max_positional_args

[lawrence_danna]

Summary

Move breakpoints from the old, bad ArgInfo::count to the new, better
ArgInfo::max_positional_args. Soon ArgInfo::count will be no more.

This functionality is tested in TestFormatters.py, TestDataFormatterSynthVal.py,
TestDataFormatterSynthType.py.

You may notice that the old code was passing 0 arguments when count was 1, and passing
1 argument when count is 2.

This is no longer necessary because max_positional_args counts the self pointer
correctly.

lldb/scripts/Python/python-wrapper.swig

 )
 {
     PythonObject self(PyRefType::Borrowed, implementor);
     auto pfunc = self.ResolveName<PythonCallable>("num_children");
 
     if (!pfunc.IsAllocated())
         return 0;
 
+    auto arg_info = pfunc.GetArgInfo();
+    if (!arg_info) {
+        llvm::consumeError(arg_info.takeError());
+        return 0;
+    }
+
     PythonObject result;
-    auto argc = pfunc.GetNumArguments();
-    if (argc.count == 1)
+
+    if (arg_info.get().max_positional_args < 1)
         result = pfunc();
-    else if (argc.count == 2)
+    else
         result = pfunc(PythonInteger(max));
 
     if (!result.IsAllocated())
         return 0;
 
     PythonInteger int_result = result.AsType<PythonInteger>();
     if (!int_result.IsAllocated())
         return 0;
 
     size_t ret_val = int_result.GetInteger();
 
-    if (PyErr_Occurred())
+    if (PyErr_Occurred()) //FIXME use Expected to catch python exceptions
     {
         PyErr_Print();
         PyErr_Clear();
     }
 
-    if (argc.count == 1)
+    if (arg_info.get().max_positional_args < 1)
         ret_val = std::min(ret_val, static_cast<size_t>(max));
 
     return ret_val;
 }
 
 SWIGEXPORT PyObject*
 LLDBSwigPython_GetChildAtIndex
 (