Adds ExpandColapse pattern to SplitButton

[ricardobossan]

Fixes #4173

Proposed changes

Customer Impact

Regression?

• Yes / No

Risk

Screenshots

Before

After

Test methodology

Accessibility testing

Test environment(s)

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.15607%. Comparing base (4419d3a) to head (92299aa).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #14092         +/-   ##
===================================================
+ Coverage   77.15603%   77.15607%   +0.00003%     
===================================================
  Files           3279        3279                 
  Lines         645317      645318          +1     
  Branches       47718       47718                 
===================================================
+ Hits          497901      497902          +1     
- Misses        143725      143732          +7     
+ Partials        3691        3684          -7     

Flag	Coverage Δ
Debug	77.15607% <100.00000%> (+0.00003%)	⬆️
integration	18.99480% <0.00000%> (+0.00307%)	⬆️
production	52.02124% <100.00000%> (+0.00016%)	⬆️
test	97.40749% <100.00000%> (ø)
unit	49.43808% <100.00000%> (-0.02587%)	⬇️

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