fix(module:qrcode): optimize demo display and nzPadding value

[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
[ ] 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

Merging #8020 (85c5a29) into master (544f308) will increase coverage by 0.00%.
The diff coverage is 85.71%.

❗ Current head 85c5a29 differs from pull request most recent head 68e7438. Consider uploading reports for the commit 68e7438 to get more accurate results

@@           Coverage Diff           @@
##           master    #8020   +/-   ##
=======================================
  Coverage   91.64%   91.65%           
=======================================
  Files         515      515           
  Lines       17637    17641    +4     
  Branches     2789     2790    +1     
=======================================
+ Hits        16164    16169    +5     
  Misses       1175     1175           
+ Partials      298      297    -1     

Impacted Files	Coverage Δ
components/qr-code/qrcode.component.ts	90.69% <85.71%> (-1.62%)	⬇️

... and 1 file with indirect coverage changes