[WIP] fix(module: tree): fix nzOnSearchChange & folder tree demo

[simplejason]

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
[x] 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

[codecov]

Codecov Report

Merging #1602 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1602      +/-   ##
==========================================
+ Coverage   96.01%   96.01%   +<.01%     
==========================================
  Files         466      466              
  Lines       11068    11069       +1     
  Branches     1456     1456              
==========================================
+ Hits        10627    10628       +1     
  Misses        125      125              
  Partials      316      316

Impacted Files	Coverage Δ
components/tree/nz-tree.component.ts	100% <100%> (ø)	⬆️
components/tree/nz-tree.service.ts	95.78% <100%> (+0.04%)	⬆️

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