fix(module:nz-alert): emit close after fade animation is done

[dmytroyarmak]

Fixes #1666

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?

nzOnClose is emitted immediately and as a result, ngIfon alert hides it before the animation is done

Issue Number: #1666

What is the new behavior?

nzOnClose is emitted only when a fade animation is finished, so you will be able to see animation if you are controlling the visibility of alert with ngIf

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #1667 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #1667      +/-   ##
=========================================
+ Coverage      96%     96%   +<.01%     
=========================================
  Files         466     466              
  Lines       11076   11078       +2     
  Branches     1459    1460       +1     
=========================================
+ Hits        10633   10635       +2     
  Misses        125     125              
  Partials      318     318

Impacted Files	Coverage Δ
components/alert/nz-alert.component.ts	100% <100%> (ø)	⬆️

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