fix(datepicker): model should be prestine on init from ngModel

[valorkin]

fixes #3014

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• added/updated tests.
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• added/updated demos.

[codecov]

Codecov Report

Merging #3115 into development will decrease coverage by 0.12%.
The diff coverage is 7.69%.

@@               Coverage Diff               @@
##           development    #3115      +/-   ##
===============================================
- Coverage        65.44%   65.31%   -0.13%     
===============================================
  Files              209      209              
  Lines             5617     5628      +11     
  Branches           988      990       +2     
===============================================
  Hits              3676     3676              
- Misses            1678     1689      +11     
  Partials           263      263

Impacted Files	Coverage Δ
...c/datepicker/bs-daterangepicker-input.directive.ts	26.66% <0%> (-2.43%)	⬇️
src/datepicker/bs-datepicker-input.directive.ts	29.09% <14.28%> (-3.57%)	⬇️

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[YevheniiaMazur]

Tested, looks good