fix(dropdown): close dropdown when focus leaves menu

[Smoggy]

fix of the issue #3140

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• read and followed the CONTRIBUTING.md guide.
• built and tested the changes locally.
• added/updated any applicable tests.
• added/updated any applicable API documentation.
• added/updated any applicable demos.

[codecov-commenter]

Codecov Report

Merging #3625 into master will decrease coverage by 0.30%.
The diff coverage is 70.58%.

@@            Coverage Diff             @@
##           master    #3625      +/-   ##
==========================================
- Coverage   91.53%   91.23%   -0.31%     
==========================================
  Files         100      100              
  Lines        2930     2988      +58     
  Branches      539      555      +16     
==========================================
+ Hits         2682     2726      +44     
- Misses        186      192       +6     
- Partials       62       70       +8     

Flag	Coverage Δ
#e2e	56.22% <70.58%> (-0.67%)	⬇️
#unit	87.75% <0.00%> (-0.65%)	⬇️

Impacted Files	Coverage Δ
src/dropdown/dropdown.ts	91.71% <70.58%> (-2.41%)	⬇️
src/nav/nav.ts	90.10% <0.00%> (-9.90%)	⬇️
src/util/positioning.ts	95.86% <0.00%> (-0.04%)	⬇️
src/nav/nav-config.ts	100.00% <0.00%> (ø)
src/modal/modal-config.ts	100.00% <0.00%> (ø)
src/modal/modal-window.ts	93.61% <0.00%> (+0.13%)	⬆️

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