fix(module:tabs): hide next and prev buttons

[wenqi73]

close #1964

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

The class ant-tabs-bar which defined in [nz-tabs-nav] host is rendered after ngAfterContentInit ( this conclusion is only according to my debugging, is there any angular mechanism to point this ? ).

ng-zorro-antd/components/tabs/nz-tabs-nav.component.ts

Line 37 in 2d123eb

'[class.ant-tabs-bar]': 'true'

showPaginationControls will get wrong result because the tabs-nav is not vertical:

so define the class in div will fix this issue.

[codecov]

Codecov Report

Merging #2239 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2239      +/-   ##
==========================================
+ Coverage   95.96%   95.97%   +<.01%     
==========================================
  Files         482      482              
  Lines       11965    11965              
  Branches     1594     1594              
==========================================
+ Hits        11482    11483       +1     
  Misses        134      134              
+ Partials      349      348       -1

Impacted Files	Coverage Δ
components/tabs/nz-tabs-nav.component.ts	91.82% <ø> (ø)	⬆️
components/tabs/nz-tabset.component.ts	96.58% <0%> (+0.85%)	⬆️

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