feat(module:select): support number as label (#6535)

[xiejay97]

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?

[ ] Bugfix
[x] 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: close #6535

What is the new behavior?

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 #6538 (a600581) into master (ddc7ded) will decrease coverage by 0.01%.
The diff coverage is 89.74%.

❗ Current head a600581 differs from pull request most recent head cc79d3d. Consider uploading reports for the commit cc79d3d to get more accurate results

@@            Coverage Diff             @@
##           master    #6538      +/-   ##
==========================================
- Coverage   89.90%   89.88%   -0.02%     
==========================================
  Files         479      481       +2     
  Lines       15319    15374      +55     
  Branches     2333     2343      +10     
==========================================
+ Hits        13772    13819      +47     
- Misses        930      937       +7     
- Partials      617      618       +1     

Impacted Files	Coverage Δ
components/core/config/config.ts	100.00% <ø> (ø)
components/modal/modal.module.ts	100.00% <ø> (ø)
components/select/select.component.ts	87.09% <57.14%> (-0.49%)	⬇️
components/modal/modal.component.ts	90.32% <62.50%> (-2.62%)	⬇️
components/mention/mention.component.ts	97.72% <75.00%> (+0.01%)	⬆️
components/dropdown/dropdown.directive.ts	88.57% <85.71%> (-0.21%)	⬇️
...ts/auto-complete/autocomplete-trigger.directive.ts	95.83% <100.00%> (+0.15%)	⬆️
components/auto-complete/autocomplete.component.ts	91.58% <100.00%> (+0.24%)	⬆️
components/cascader/cascader.component.ts	94.62% <100.00%> (+0.01%)	⬆️
components/date-picker/date-picker.component.ts	93.46% <100.00%> (+0.04%)	⬆️
... and 19 more

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[vthinkxie]

lgtm

[xiejay97]

@vthinkxie 应该去检查label等于0的情况，需要修复 🙏