[new feature] Stepper: add button-size prop

[chenjiahan]

No description provided.

[codecov-io]

Codecov Report

Merging #3714 into dev will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##              dev   #3714      +/-   ##
=========================================
+ Coverage   93.17%   93.2%   +0.03%     
=========================================
  Files         124     124              
  Lines        2683    2695      +12     
  Branches      248     248              
=========================================
+ Hits         2500    2512      +12     
  Misses        151     151              
  Partials       32      32

Impacted Files	Coverage Δ
src/stepper/index.js	100% <100%> (ø)	⬆️

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