fix(input[date]): support years with more than 4 digits

[gkalpak]

Currently, (mainly because of the REGEXPs used for parsing dates, e.g. here and there), date-family inputs do not support years with more than 4 digits (they consider the value invalid and the parser returns undefined).

According to the W3 spec, the value of a date-family input should be a "valid full-date as defined in [RFC 3339], with the additional qualification that the year component is four or more digits representing a number greater than 0" _{(emphasis mine)}.

Additionally, ISO 8601 allows (upon agreement of the involved parties) to have expanded representation of years (with more than 4 digits); see for example sections 2.3.8 and 4.1.2.4.

Current browser support:

• Chrome, Opera: Support date inputs and years greater than 9999.
• Firefox, IE: Do not support date inputs, but the user can still enter the dates in ISO format and ngModel parses them correctly
• Edge: Supports date inputs, but not years greater than 9999.
• Safari: ???

There's nothing we can do for MS Edge on the Angular side, but the users of other browsers will still benefit from adding support for years greater than 9999.

[Narretz]

Safari 9 has no special date input handling. ios9 has a datepicker input, and you can't actually enter the date by hand (at least not in Saucelabs).