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

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

It looks like this functionality is already well tested by
`TestBreakpointCommandsFromPython.py`, so there's no need to write
additional tests for it.

Reviewers: labath, jingham, JDevlieghere

Reviewed By: labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D69468

lldb/unittests/ScriptInterpreter/Python/PythonTestSuite.cpp

@@ -59,7 +59,7 @@ extern "C" void init_lldb(void) {}
 #define LLDBSwigPyInit init_lldb
 #endif
 
-extern "C" bool LLDBSwigPythonBreakpointCallbackFunction(
+extern "C" llvm::Expected<bool> LLDBSwigPythonBreakpointCallbackFunction(
     const char *python_function_name, const char *session_dictionary_name,
     const lldb::StackFrameSP &sb_frame,
     const lldb::BreakpointLocationSP &sb_bp_loc,