fix(module:button): fix order of DOM nodes in button

[vthinkxie]

close #3079

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
[ ] No

Other information

[netlify]

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Deploy preview for ng-zorro-master ready!

Built with commit 834c2c8

https://deploy-preview-3578--ng-zorro-master.netlify.com

[codecov]

Codecov Report

Merging #3578 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3578      +/-   ##
==========================================
+ Coverage    95.7%   95.73%   +0.02%     
==========================================
  Files         690      690              
  Lines       13699    13708       +9     
  Branches     1823     1824       +1     
==========================================
+ Hits        13111    13123      +12     
+ Misses        200      198       -2     
+ Partials      388      387       -1

Impacted Files	Coverage Δ
components/button/nz-button.component.ts	95% <100%> (+0.63%)	⬆️
components/select/nz-option-container.component.ts	97.67% <0%> (+2.32%)	⬆️
components/core/util/dom.ts	91.17% <0%> (+5.88%)	⬆️

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