fix(module:datepicker): focus input when opened programmatically

[sebcam]

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?

When opening a datepicker by code using open() function, the picker open fine but the picker input is not focused, involving problems to exit picker.
Can be reproduce on the customized range picker exemple here

Issue Number: N/A

What is the new behavior?

When opening by code, picket input get focused if not already.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #7512 (15d3252) into master (3680ed9) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7512      +/-   ##
==========================================
+ Coverage   91.71%   91.72%   +0.01%     
==========================================
  Files         502      502              
  Lines       16697    16698       +1     
  Branches     2606     2752     +146     
==========================================
+ Hits        15314    15317       +3     
+ Misses       1050     1049       -1     
+ Partials      333      332       -1     

Impacted Files	Coverage Δ
components/date-picker/date-picker.component.ts	92.60% <100.00%> (+0.02%)	⬆️
components/tabs/tab-nav-bar.component.ts	87.94% <0.00%> (+0.70%)	⬆️

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[wenqi73]

LGTM.