fix: improve gradle build cache stability

[simschla]

As I reported in #101 we have issues when using gradle remote build cache: Sometimes (not always) we get cache misses due to fingerprint differences for options.compilerArgumentProviders.errorprone$0 and options.compilerArgumentProviders.errorprone$0.errorproneOptions.

I was not very successful with debugging the issue (it is non-trivial). Using the changes in this PR, I am no longer seeing these fingerprint differences between CI and developer machines. It has been consistently working for us for the last 100+ builds.

Feel free to deny this PR or request more changes if you don't feel confident about it @tbroyer

[simschla]

@tbroyer Anything else I can do on my side?

[tbroyer]

Did you bring the issue up to the Gradle team?

I stand by my comment I'm afraid: AFAICT it's supposed to work, so if it doesn't it looks like a bug in Gradle (unless they say it's not actually supposed to work and provide guidance) and/or something specific to your environment.
…and they do use the plugin themselves as part of Gradle's own build (that uses a build cache), and inside smoke tests.

[simschla]

I have not reached out to the gradle team, will do and report back here.