[time-picker] Enable simple value parsing

[juuso-vaadin]

Describe your motivation

Being able to type in just numbers without separators would allow faster input and improve the UX.
Time is something that can be expected to be primarily typed in rather that picked from list of options.

Describe the solution you'd like

Inputting "1245" should result "12:45".

Additionally it would be nice if both "0945" and "945" would result "09:45".

Additional context

<input type="time"> doesn't require typing in the separators.
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/time

[rolfsmeds]

Custom parsing formats should be implemented together with custom presentation formats: #1030.