map add drop event

[deyihu]

fix #2105

[codecov-commenter]

Codecov Report

Merging #2106 (84d39e1) into master (dfdb231) will decrease coverage by 0.03%.
Report is 3 commits behind head on master.
The diff coverage is 33.33%.

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@@            Coverage Diff             @@
##           master    #2106      +/-   ##
==========================================
- Coverage   83.43%   83.41%   -0.03%     
==========================================
  Files         164      164              
  Lines       18301    18313      +12     
==========================================
+ Hits        15270    15275       +5     
- Misses       3031     3038       +7     

Files	Coverage Δ
src/map/Map.js	87.21% <ø> (ø)
src/map/Map.DomEvents.js	85.24% <33.33%> (-5.67%)	⬇️

... and 1 file with indirect coverage changes

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[fuzhenn]

感觉可以直接在 Map.DomEvents.js 中增加对这几个新增事件的注册就可以了，不需要单独实现