feat: added "excludeDisabledDays" prop for range picker

[benoitgoupilleau]

Context

I'm planning to use react-day-picker for a booking website and typically I would use the range picker. Days that are already booked would appear as disabled but the current package let the user pick a range with potentially disabled days inside.
In that particular use-case, it doesn't work as a booking can't overlap another one.

Analysis

Current code only disables dates for clicking on it, so when a user selects a range, the from can be before a disabled date and the to after, hence selecting a disabled date. In a case of a booking website, that would mean someone could double book.

Solution

My solution is to pass a boolean excludeDisabledDays as prop and if true, the modifiers.disabled will be updated with the enclosing disabled dates. Hence if the user selects a date before a disabled date, then all the dates after that disabled date will be also disabled. The function findDisabledDays looks for the closest disabled dates after and before the selected date and that result is used to update the disabled dates accordingly.
The function addToRange had to be updated as with a min provided, the user could have ended up in the situation where no other dates could be selected. Clicking again on the selected date will now clear the range.

[gpbl]

@benoitgoupilleau thanks for your work here! I don't think a new prop is idea to fix the bug - the exposed solution here should be the default behavior.

The changes proposed may have impact over the performances - reason I haven't merged this yet. I'll keep this open to review it in the next future.