multi method
Reads a repeatable option, with blanks dropped.
A blank arrives from --platform '' or from a trailing comma in
--platform linux-x64,, neither of which should become a selector that
matches nothing.
Implementation
List<String> multi(String name) => [
for (final value in argResults?.multiOption(name) ?? const <String>[])
if (value.trim().isNotEmpty) value.trim(),
];