feat(module:skeleton): support for square shape of skeleton button

[HyperLife1119]

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?

Waiting for #8479.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.61%. Comparing base (d2917e6) to head (3aa166d).
Report is 17 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8481   +/-   ##
=======================================
  Coverage   91.60%   91.61%           
=======================================
  Files         532      532           
  Lines       18399    18399           
  Branches     2813     2813           
=======================================
+ Hits        16855    16856    +1     
+ Misses       1228     1227    -1     
  Partials      316      316           

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[Nicoss54]

LGTM

[OriginRing]

LGTM