Enable source code browsing

[tempora-mutantur]

When we enabling source file browsing, Code Coverage API plugin will add paint information to CoverageResult and copy and render these source files to the build directory.

If we want to show those source files on the result page, we need to invoke setRelativeSourcePath to set the mapped source file for the CoverageResult. In our case, we might need to add the source file path as an attribute to Class element and set it in our parser

See https://github.com/jenkinsci/code-coverage-api-plugin/blob/dev/src/main/java/io/jenkins/plugins/coverage/adapter/parser/JavaCoverageParser.java#L74 as an example.