fix(module:core): outside click closed the lower overlay

[hsuanxyz]

close #6060

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

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #6064 (70c5f48) into master (3204927) will increase coverage by 0.01%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##           master    #6064      +/-   ##
==========================================
+ Coverage   89.89%   89.90%   +0.01%     
==========================================
  Files         465      466       +1     
  Lines       14057    14063       +6     
  Branches     2311     2310       -1     
==========================================
+ Hits        12636    12644       +8     
  Misses        873      873              
+ Partials      548      546       -2     

Impacted Files	Coverage Δ
components/core/overlay/nz-overlay.module.ts	100.00% <ø> (ø)
components/date-picker/picker.component.ts	89.47% <ø> (ø)
components/popconfirm/popconfirm.ts	100.00% <ø> (ø)
components/popover/popover.ts	92.85% <ø> (ø)
components/select/select.component.ts	88.25% <ø> (+0.54%)	⬆️
components/time-picker/time-picker.component.ts	87.20% <ø> (+1.26%)	⬆️
components/tooltip/base.ts	91.28% <ø> (-0.14%)	⬇️
components/tooltip/tooltip.ts	100.00% <ø> (ø)
components/tree-select/tree-select.component.ts	93.46% <ø> (-0.10%)	⬇️
components/mention/mention.component.ts	97.61% <50.00%> (-0.57%)	⬇️
... and 6 more

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[wzhudev]

https://zhuanlan.zhihu.com/p/364776062 Will this be helpful?