feat(module:dropdown): improve NzContextMenuService#create()

[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

NzContextMenuService#create() return void，developer cannot listen to view destroy event.

What is the new behavior?

NzContextMenuService#create() will now return EmbeddedViewRef, developers can listen to view destroy event through EmbeddedViewRef#onDestroy().

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 #7768 (d90eb41) into master (37391de) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head d90eb41 differs from pull request most recent head 678bf15. Consider uploading reports for the commit 678bf15 to get more accurate results

@@            Coverage Diff             @@
##           master    #7768      +/-   ##
==========================================
- Coverage   91.68%   91.66%   -0.02%     
==========================================
  Files         515      515              
  Lines       17634    17634              
  Branches     2789     2789              
==========================================
- Hits        16168    16165       -3     
- Misses       1170     1172       +2     
- Partials      296      297       +1     

Impacted Files	Coverage Δ
components/dropdown/context-menu.service.ts	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[HyperLife1119]

It's ready.

[wzhudev]

LGTM

[wzhudev]

Thanks for contributing. A test case would be better :)

[HyperLife1119]

This PR is ready to be merged. @simplejason @wzhudev @OriginRing