feat: allow to customize table expand icon

[twisger]

antd #10819

[codecov-io]

Codecov Report

Merging #237 into master will increase coverage by 0.04%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #237      +/-   ##
==========================================
+ Coverage   93.38%   93.43%   +0.04%     
==========================================
  Files          17       17              
  Lines         726      731       +5     
  Branches      208      212       +4     
==========================================
+ Hits          678      683       +5     
  Misses         40       40              
  Partials        8        8

Impacted Files	Coverage Δ
src/ExpandableTable.js	98.21% <ø> (ø)	⬆️
src/ExpandIcon.js	100% <100%> (ø)	⬆️
src/ExpandableRow.js	97.61% <100%> (+0.18%)	⬆️

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[afc163]

ant-design/ant-design#11802

[yesmeck]

#236