fix: early stopping test and average precision metric

[imatiach-msft]

• re-enable early stopping test
• add average precision metric to comparison logic for early stopping

[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov]

Codecov Report

Merging #1034 (f37b231) into master (04a9876) will increase coverage by 0.38%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1034      +/-   ##
==========================================
+ Coverage   84.50%   84.88%   +0.38%     
==========================================
  Files         203      203              
  Lines        9639     9640       +1     
  Branches      585      559      -26     
==========================================
+ Hits         8145     8183      +38     
+ Misses       1494     1457      -37     

Impacted Files	Coverage Δ
...a/com/microsoft/ml/spark/lightgbm/TrainUtils.scala	86.40% <100.00%> (+9.13%)	⬆️
...m/microsoft/ml/spark/lightgbm/LightGBMParams.scala	89.57% <0.00%> (+1.42%)	⬆️
.../microsoft/ml/spark/lightgbm/LightGBMBooster.scala	89.06% <0.00%> (+1.56%)	⬆️
...com/microsoft/ml/spark/core/contracts/Params.scala	95.65% <0.00%> (+4.34%)	⬆️

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[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[imatiach-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[mhamilton723]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).