On argument swapping to put positional ones toward the end,
m_arg_index was pointing at "last arg index" + "skipped args" +
"consumed args" and thus was pointing ahead of the skipped ones.
m_arg_index now points after the current parsed option arguments.
This commit moves the implementation of getopt into AK, and converts its
API to understand and use StringView instead of char*.
Everything else is caught in the crossfire of making
Option::accept_value() take a StringView instead of a char const*.
With this, we must now pass a Span<StringView> to ArgsParser::parse(),
applications using LibMain are unaffected, but anything not using that
or taking its own argc/argv has to construct a Vector<StringView> for
this method.
