fix(module:auto-complete, mention, tree-select): update cdk overlay positioning strategy

[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: #1756

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1761 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #1761   +/-   ##
=======================================
  Coverage   96.05%   96.05%           
=======================================
  Files         466      466           
  Lines       11146    11146           
  Branches     1456     1456           
=======================================
  Hits        10706    10706           
  Misses        127      127           
  Partials      313      313

Impacted Files	Coverage Δ
components/mention/mention.component.ts	99.41% <100%> (ø)	⬆️
...auto-complete/nz-autocomplete-trigger.directive.ts	96.68% <100%> (ø)	⬆️
components/tree-select/nz-tree-select.component.ts	99.03% <100%> (ø)	⬆️

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