Add Scala support for Gradle projects

[olafurpg]

Currently, the lsif-java index command can only index Scala projects using sbt. It would be nice to add support to index Scala projects using Gradle as well.

[olafurpg]

I started working on this feature and made some progress, behold the first Gradle build with hybrid Scala/Java codebases where lsif-java index handles both Java and Scala

https://sourcegraph.com/github.com/apache/samza@a7cb039d2d53cbcf207a12fce504066da8bc21cb/-/blob/samza-kv/src/main/scala/org/apache/samza/storage/kv/LoggedStore.scala?L38:69#tab=references

[olafurpg]

Released https://github.com/sourcegraph/lsif-java/releases/tag/v0.6.8