[lldb/Python] Make use of PythonObject and PythonFormat in callbacks (NFC)
This patch extends the template specialization of PythonFormat structs
and makes use of the pre-existing PythonObject class to format arguments
and pass them to the right method, before calling it.
This is a preparatory patch to merge PythonFormat with SWIGPythonBridge's
GetPythonValueFormatString methods.
Differential Revision: https://reviews.llvm.org/D138248
Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>