fix(module:drawer): should clear previously focused element

[ParsaArvanehPA]

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
• 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?

When a drawer is opened, the previously focused element is saved. This allows the element to be refocused when the drawer is closed. If no element was previously focused, the new focused element is set upon opening the drawer. In this case, the previous focus value is cleared. So by clearing the value upon closing the drawer, the correct behavior is acheived.

Issue Number: #8839

What is the new behavior?

Does this PR introduce a breaking change?

• Yes
• No

Other information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.89%. Comparing base (68f6324) to head (3dde607).
Report is 50 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8893      +/-   ##
==========================================
- Coverage   91.94%   91.89%   -0.06%     
==========================================
  Files         537      546       +9     
  Lines       18455    19292     +837     
  Branches     2816     2850      +34     
==========================================
+ Hits        16969    17728     +759     
- Misses       1182     1252      +70     
- Partials      304      312       +8     

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