feat(module:float-button): add float-button component

[OriginRing]

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?

Issue Number: N/A

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

Attention: Patch coverage is 87.91946% with 18 lines in your changes missing coverage. Please review.

Project coverage is 91.85%. Comparing base (5fec53e) to head (792dec0).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...nents/float-button/float-button-group.component.ts	81.48%	8 Missing and 2 partials ⚠️
...ponents/float-button/float-button-top.component.ts	91.17%	5 Missing and 1 partial ⚠️
components/float-button/float-button.component.ts	90.90%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7884      +/-   ##
==========================================
+ Coverage   91.84%   91.85%   +0.01%     
==========================================
  Files         537      542       +5     
  Lines       18472    18620     +148     
  Branches     2815     2828      +13     
==========================================
+ Hits        16965    17103     +138     
- Misses       1204     1209       +5     
- Partials      303      308       +5     

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[NRaf]

Hi,

Just came across this feature in the React branch and noticed it's missing from ng-zorro. Any idea on when this will be merged in?

[Laffery]

LGTM

[lppedd]

Just wondering, does that mean the backtop component is to be considered deprecated?
Is it in preparation for Ant Design 5?