feat(module:core,dropdown,table): add config for backdrop

[QichenZhu]

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: #6951

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #6783 (c198829) into master (d1cdd0e) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #6783    +/-   ##
========================================
  Coverage   89.61%   89.61%            
========================================
  Files         488      488            
  Lines       15778    15783     +5     
  Branches     2568     2423   -145     
========================================
+ Hits        14139    14144     +5     
  Misses        997      997            
  Partials      642      642            

Impacted Files	Coverage Δ
components/core/config/config.ts	100.00% <ø> (ø)
components/dropdown/dropdown.directive.ts	88.78% <100.00%> (+0.32%)	⬆️
...onents/table/src/addon/filter-trigger.component.ts	45.83% <100.00%> (+4.92%)	⬆️

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[wzhudev]

LGTM