parseStrict method
Given user input, attempt to parse the inputString into the anticipated
format, treating it as being in the local timezone.
If inputString does not match our format, throws a FormatException.
This will reject dates whose values are not strictly valid, even if the
DateTime constructor will accept them. It will also rejct strings with
additional characters (including whitespace) after a valid date. For
looser parsing, use parse.
Implementation
DateTime parseStrict(String inputString, [utc = false]) =>
_parse(inputString, utc: utc, strict: true);