feat(module:cascader): Add search

[wzhudev]

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?

User can search in Cascader now.

Issue Number: #1773

What is the new behavior?

User can search options by inputing.

Does this PR introduce a breaking change?

[] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1873 into master will increase coverage by 0.02%.
The diff coverage is 97.22%.

@@            Coverage Diff            @@
##           master   #1873      +/-   ##
=========================================
+ Coverage   95.97%     96%   +0.02%     
=========================================
  Files         466     466              
  Lines       11217   11286      +69     
  Branches     1474    1493      +19     
=========================================
+ Hits        10766   10835      +69     
  Misses        131     131              
  Partials      320     320

Impacted Files	Coverage Δ
components/cascader/nz-cascader.component.ts	96.3% <97.22%> (+0.3%)	⬆️
components/tabs/nz-tabset.component.ts	96.58% <0%> (+0.85%)	⬆️

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