fix(module:mention): unable to select on mobile device

[hsuanxyz]

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: #4281

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

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[codecov]

Codecov Report

Merging #4309 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4309      +/-   ##
==========================================
+ Coverage   92.15%   92.16%   +<.01%     
==========================================
  Files         520      520              
  Lines       11016    11017       +1     
  Branches     1997     1998       +1     
==========================================
+ Hits        10152    10154       +2     
  Misses        431      431              
+ Partials      433      432       -1

Impacted Files	Coverage Δ
components/mention/nz-mention.component.ts	98.6% <100%> (ø)	⬆️
components/time-picker/time-holder.ts	96.49% <0%> (+0.87%)	⬆️

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