RangeCalendar format propType to work with array

[onlyann]

The format prop accepts both string and string[].

Update the format prop type to match the underlying CalendarPart component.

Without this change, passing an array of formats to the RangeCalendar component works but results in a warning.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.78%. Comparing base (d486704) to head (00dd145).
⚠️ Report is 15 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #613   +/-   ##
=======================================
  Coverage   90.78%   90.78%           
=======================================
  Files          10       10           
  Lines         716      716           
  Branches      214      214           
=======================================
  Hits          650      650           
  Misses         57       57           
  Partials        9        9           

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