skip non-class files in the exclusions processing for MergeJars

[vinnybod]

This is sort of an addendum to #1106 and #1107
In the previous PR, I added an exception for COPYRIGHT and NOTICE since it was the same kind of use case as the existing LICENSE exception.

The issue that I am having is that I have files that should be present in all of the jars being published in a repo that are not COPYRIGHT, NOTICE, or LICENSE. For example a project-version.properties file that contains info about the build.

Changing the readExcludedFileNames function to only process *.class files allows for these files to propagate to the final jar. It also still passes all existing test cases.

The only test for this functionality is specifically looking at .class files.https://github.com/bazelbuild/rules_jvm_external/blob/master/tests/com/github/bazelbuild/rules_jvm_external/jar/MergeJarsTest.java#L221

I am open to other solutions, but this seems to have fixed a lot of issues for my use case without breaking any existing functionality that is being tested for.

[shs96c]

How would this cope with multiple versions of the same file? Things like log4j config files, or other elements that are often found in the root directory of a jar, and that could (would!) cause problems.

[vinnybod]

This would still handle those duplicate files however the --duplicates flag is set, which defaults to last-wins. I added two additional tests to the pull request to show that behavior.

To me, this makes more sense than the existing behavior which is excluding files completely. I’m not 100% sure why the exclusions work the way they do. But, I don’t have the full picture of this tool, so please let me know me if I am missing anything.

Specifically, the case I am running into is with java_export. The lib that gets created has the files I expect, but then after the -project jar is generated, it is missing files.