DrawTool support set layer zIndex

[deyihu]

fix #2072

[codecov-commenter]

Codecov Report

Merging #2073 (15cb954) into master (9db0e54) will decrease coverage by 0.06%.
The diff coverage is 67.64%.

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@@            Coverage Diff             @@
##           master    #2073      +/-   ##
==========================================
- Coverage   83.94%   83.88%   -0.06%     
==========================================
  Files         164      164              
  Lines       18085    18117      +32     
==========================================
+ Hits        15181    15198      +17     
- Misses       2904     2919      +15     

Files Changed	Coverage Δ
src/map/tool/DrawTool.js	76.62% <62.06%> (-1.88%)	⬇️
src/map/tool/DistanceTool.js	80.27% <100.00%> (+0.41%)	⬆️

... and 2 files with indirect coverage changes

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