Add Java Formatter to Gradle Tasks

[0xjjoyy]

When contributing it's easier if there is a gradle task that can take care of formatting the Java files according to the project's desired format, rather than manually maintaining the format and manually correcting checkstyle errors.

Doing a clean checkout and running the gradle tasks doesn't show any Java file formatter

./gradlew tasks

Please add a Java File formatter plugin to this project that conforms to the project's desired style, so it'll be easier and faster to make pull requests and contributions. Please also do a one time run over the entire project, so the entire project is consistently formatted.

[JordonPhillips]

We're experimenting with a formatter in a separate project, once we get it to a place we like we'll migrate it over.

[haydenbaker]

With #2485, this is now a reality. The formatter will run on the build task, or can be ran manually with spotlessApply.