Add a predicate in DateRangePickerMonthViewSettings for example called "isDateSelectable" that allows us to return a boolean indicating whether a certain date is selectable or not (should be called for any dates currently active on the screen.)
Use case:
Currently, blackOutDates is just a list of dates which allows us to supply a list of dates to black out but it precludes scenarios where for example I want to allow only Mondays to be selected.
The only way we can do that currently is to rebuild the widget and its blackOutDates property from inside the onViewChanged callback which is a viable workaround but causes the entire widget to be rebuild no matter the state management solution on hand.