This is required for HTMLDateTimeField to be compatible it:
HTMLDateTimeField filters out mustBeAfter/mustBeBefore, while
DateInputWidget didn’t understand min/max until now. Since moment.js
(used by the JavaScript side of the widget) seems to better like the
mustBeAfter/mustBeBefore semantics (strictly larger/smaller than) than
the min/max one (larger/smaller than or equal to), I decided to
internally keep mustBeAfter/mustBeBefore.
Bug: T219633
Change-Id: I487363e40d1e4f74780ed7146c8a6770bfc61fae
ce8e8894bd