fix(module:datepicker): send OnChange event for same value

[Nicoss54]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

valueChange/ngModelChange is notified event if value don't change

Issue Number: #7814

What is the new behavior?

valueChange / ngModelChange is not notified anymore if value not change

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #7815 (9e07e67) into master (445d183) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #7815   +/-   ##
=======================================
  Coverage   92.09%   92.10%           
=======================================
  Files         502      502           
  Lines       16808    16819   +11     
  Branches     2573     2577    +4     
=======================================
+ Hits        15480    15491   +11     
  Misses       1056     1056           
  Partials      272      272           

Impacted Files	Coverage Δ
components/date-picker/date-picker.component.ts	94.64% <100.00%> (+0.18%)	⬆️

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[wenqi73]

LGTM