fix(module:cascader): hide placeholder when trigger compositionstart

[Zz-ZzzZ]

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
• 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: #8533

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[zorro-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.51%. Comparing base (20bb5b2) to head (7ed423d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8641      +/-   ##
==========================================
- Coverage   91.52%   91.51%   -0.01%     
==========================================
  Files         535      535              
  Lines       18411    18416       +5     
  Branches     2904     2904              
==========================================
+ Hits        16850    16853       +3     
- Misses       1241     1242       +1     
- Partials      320      321       +1     

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[HyperLife1119]

LGTM