fix(module:message): clean up DOM after usage

[swseverance]

Call overlayRef.dispose() when all instances of messages have disappeared

Resolves #7772

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?

The current implementation of the message service leaves a nz-message-container element in the DOM even after all messages have been removed. This PR introduces a small change so that the DOM is cleaned up when all messages are removed, so no extra elements remain in the DOM

[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?

Issue Number: #7772

What is the new behavior?

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

Merging #7965 (0c03c20) into master (544f308) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 0c03c20 differs from pull request most recent head 553f02d. Consider uploading reports for the commit 553f02d to get more accurate results

@@            Coverage Diff             @@
##           master    #7965      +/-   ##
==========================================
- Coverage   91.64%   91.63%   -0.02%     
==========================================
  Files         515      515              
  Lines       17637    17652      +15     
  Branches     2789     2791       +2     
==========================================
+ Hits        16164    16175      +11     
- Misses       1175     1179       +4     
  Partials      298      298              

Impacted Files	Coverage Δ
components/core/services/singleton.ts	88.23% <100.00%> (+2.52%)	⬆️
components/message/base.ts	97.01% <100.00%> (+3.57%)	⬆️

... and 3 files with indirect coverage changes

[swseverance]

Hi @Laffery do you mind taking a look at my PR? Thanks

[swseverance]

@simplejason do you mind taking a look? Thank you

[simplejason]

@simplejason do you mind taking a look? Thank you

Thanks for your contributions, it looks good for me, please rebase your brach with the master branch, after that I will merge it :) @Nicoss54 It would be great to hear your thoughts if you have the time!

[Nicoss54]

@simplejason do you mind taking a look? Thank you

Thanks for your contributions, it looks good for me, please rebase your brach with the master branch, after that I will merge it :) @Nicoss54 It would be great to hear your thoughts if you have the time!

@simplejason i take the point ;)