feat(module:select): add string array support for nzDropdownClassName

[ousc]

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?

NzDropdownClassName only support string.

Issue Number: #7611

What is the new behavior?

nzDropdownClassName supports both string and string[].

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 #7643 (f21e76f) into master (aec94c9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #7643   +/-   ##
=======================================
  Coverage   92.02%   92.03%           
=======================================
  Files         502      502           
  Lines       16750    16750           
  Branches     2632     2632           
=======================================
+ Hits        15415    15416    +1     
+ Misses       1065     1064    -1     
  Partials      270      270           

Impacted Files	Coverage Δ
components/select/select.component.ts	91.29% <100.00%> (ø)
components/core/util/text-measure.ts	92.98% <0.00%> (+0.87%)	⬆️

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[simplejason]

LGTM