Userland+AK: Stop using getopt() for ArgsParser

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.

Userland/Utilities/rm.cpp

@@ -32,7 +32,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     args_parser.parse(arguments);
 
     if (!force && paths.is_empty()) {
-        args_parser.print_usage(stderr, arguments.argv[0]);
+        args_parser.print_usage(stderr, arguments.strings[0]);
         return 1;
     }