process-util: introduce get_process_cmdline_strv()

process-util: introduce get_process_cmdline_strv()

The reason why get_process_cmdline() is so complicated is that we
need to escape and quote arguments for building a single result
string.

That's necessary when we want to log or print the command line.
However, when we want to parse the command line, it is not necessary
that the result is a single string, but can be strv.

This will be used when we parse the command line.