fix(module:watermark): removing the watermark fails to redraw

[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?

[x] 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?

MutationObserver 无法监听当前demo的删除事件

What is the new behavior?

监听往上移一层，事件处理时判断是否为水印节点后再进行重绘

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[zorro-bot]

This preview will be available after the AzureCI is passed.

[codecov]

Codecov Report

Merging #8012 (1fcfa57) into master (605e969) will increase coverage by 91.69%.
The diff coverage is 100.00%.

❗ Current head 1fcfa57 differs from pull request most recent head a1036e6. Consider uploading reports for the commit a1036e6 to get more accurate results

@@             Coverage Diff             @@
##           master    #8012       +/-   ##
===========================================
+ Coverage        0   91.69%   +91.69%     
===========================================
  Files           0      514      +514     
  Lines           0    17573    +17573     
  Branches        0     2780     +2780     
===========================================
+ Hits            0    16114    +16114     
- Misses          0     1164     +1164     
- Partials        0      295      +295     

Impacted Files	Coverage Δ
components/date-picker/date-picker.component.ts	95.25% <100.00%> (ø)
components/water-mark/water-mark.component.ts	89.23% <100.00%> (ø)

... and 512 files with indirect coverage changes