[stable31] fix(files): Add smooth animation via clicking on heading

[backportbot]

Backport of #7197

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 58.67%. Comparing base (e494d87) to head (812e44e).
Report is 2 commits behind head on stable31.

Files with missing lines	Patch %	Lines
src/components/Editor/TableOfContents.vue	0.00%	3 Missing ⚠️
src/plugins/headingAnchor.js	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           stable31    #7320      +/-   ##
============================================
+ Coverage     51.67%   58.67%   +7.00%     
============================================
  Files           290      289       -1     
  Lines         41043    36146    -4897     
  Branches        840      839       -1     
============================================
  Hits          21208    21208              
+ Misses        19715    14819    -4896     
+ Partials        120      119       -1     

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