fix: gen-build-spec maven/gradle cli parsers failed to parse valid command lines with intermixed positional args and options

[nicallen]

Summary

The maven and gradle cli parsers used by the gen-build-spec command fail to parse valid command lines with intermixed positional args and options. This change fixes that limitation.

Description of changes

Use argparse.ArgumentParser.parse_intermixed_args instead of argparse.ArgumentParser.parse_args to enable handling of intermixed args, and add a unit test case for the maven parser and for the gradle parser.

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