[lldb/crashlog] Replace deprecated optparse by argparse (NFC)

This patch replace the deprecated `optparse` module used for the
`crashlog`& `save_crashlog` commands with the new `argparse` from the
python standard library. This provides many benefits such as showing the
default values for each option in the help description, but also greatly
improve the handling of position arguments.

Differential Revision: https://reviews.llvm.org/D157849



Signed-off-by: Med Ismail Bennani <ismail@bennani.ma>