stringIgnoreCase function
Returns a parser that accepts the string element ignoring the case.
For example, stringIgnoreCase('foo') succeeds and consumes the input
string 'Foo' or 'FOO'. Fails for any other input.
Implementation
@useResult
Parser<String> stringIgnoreCase(String element, [String? message]) => predicate(
element.length,
(value) => equalsIgnoreAsciiCase(element, value),
message ?? '"$element" (case-insensitive) expected');