Allow human-friendly date/time formats in input[date] and input[datetime-local]

[PawelDecowski]

Currently, for example, input[datetime-local] requires the input to be in the format yyyy-MM-ddTHH:mm:s (documentation for input[datetime-local]) which in most cases is useless for end users.

The date/time inputs should allow custom formatting (while the model remains a Date object).

[Narretz]

I agree that the current state is not pretty. I think this could be a good fit for a third-party module, though (implemented via parsers / formatters):

• browser support is still fragmented for the date input, so many people will still use full fledged date pickers. Then again, chrome already has a date picker
• there are many different date formats, multiplied by locales. This would be a heavy burden on the core