fix(module:date-picker): use fixed width when "nzShowTime" settled fo…

[wilsoncook]

…r picker

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?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #2236 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2236      +/-   ##
==========================================
+ Coverage   95.96%   95.96%   +<.01%     
==========================================
  Files         482      482              
  Lines       11965    11972       +7     
  Branches     1594     1597       +3     
==========================================
+ Hits        11482    11489       +7     
  Misses        134      134              
  Partials      349      349

Impacted Files	Coverage Δ
...ponents/date-picker/date-range-picker.component.ts	87.03% <100%> (+1.93%)	⬆️

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