[Proposal] Fix bug for instead of overwrite, we should aggregate multiple coverage file coverage line contains same class

[BoyangTian-Robinhood]

we notice that for different test package we could have same class information for coverage with different line hit. For src/main/java/com/uber/jenkins/phabricator/coverage/XmlCoverageProvider.java computeLineCoverage method we shouldn't directly do lineCoverage.put(entry.getKey(), sortedCounts);