Android Gradle 3.5.3 doesn't clean the desugared local JARs directory

One of my Gradle plugins helps swap out a handful of JAR dependencies in Android projects. I noticed that after using it for a while on an Android Gradle 3.5.3 project, building an APK would eventually start failing with a "program type already present" error.

I determined that the problem occurred when two copies of the same JAR dependency ended up in the external_file_lib_dex_archives intermediates directory. Files there are named with a combination of a number (increasing within one run) and the original filename. I observed the same JAR with different numbers, presumably from different builds. That directory is populated by DexFileDependenciesTask, which from reading the code does not seem to ever clean its output. So if the order of JARs changes or if one is removed, extra JARs will remain and clog up the dexer.

I worked around this in my plugin by registering a doFirst action on all DexFileDependenciesTasks that deletes and recreates the task's output directory.