Fix date range Angular form control statuses

[Blackbaud-SteveBrush]

I added some unit tests to verify correct Angular form control statuses (dirty, pristine, etc.) are being applied when a user provides a date via text input and when selecting a date from the calendar.

[codecov]

Codecov Report

Merging #44 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #44   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          26     26           
  Lines        1314   1315    +1     
  Branches      200    200           
=====================================
+ Hits         1314   1315    +1

Impacted Files	Coverage Δ
...c/modules/datepicker/datepicker-input.directive.ts	100% <100%> (ø)	⬆️

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