Add pipeline task to push coverage results to coveralls (#5461)

azure-pipelines-windows.yml

@@ -32,6 +32,10 @@ steps:
     .\scripts\test.bat --reporter mocha-junit-reporter --coverage
   displayName: 'Test'
 
+- script: |
+    cat .\.build\coverage\lcov.info | node .\node_modules\coveralls\bin\coveralls.js
+  displayName: 'Upload coverage to Coveralls'
+
 - task: PublishTestResults@2
   inputs:
     testResultsFiles: 'test-results.xml'