feat(module:modal): auto focus when open and restore focus when close

[hsuanxyz]

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: #2124

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #2188 into master will decrease coverage by 0.01%.
The diff coverage is 88.88%.

@@            Coverage Diff             @@
##           master    #2188      +/-   ##
==========================================
- Coverage   95.96%   95.95%   -0.02%     
==========================================
  Files         482      482              
  Lines       11965    11983      +18     
  Branches     1594     1598       +4     
==========================================
+ Hits        11482    11498      +16     
  Misses        134      134              
- Partials      349      351       +2

Impacted Files	Coverage Δ
components/modal/nz-modal.component.ts	95.31% <88.88%> (-0.54%)	⬇️

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