Google-java-format is an open source formatter [1]. It automatically formats
source code based on the Google Java Style.

The Mockito source code to a very large extent already adheres to this style
guide. While this PR in itself is large, many of the changes are related to
string formatting and nested method calls. Most notably, google-java-format
is an improvement over the current formatting strategy in that:

1. It handles comment formatting (e.g. spacing between comments)
2. It handles nested method calls. You can see the difference in
our usage of the ByteBuddy API, which is now more consistent
3. It enforces the max-line length.

It essentially automates all of the styling rules we list in
https://github.com/mockito/mockito/blob/release/3.x/.github/CONTRIBUTING.md#alignment
As such, for new contributors it should be a lot easier (and less scary)
to contribute to Mockito, as they no longer have to be concerned about
formatting. Hopefully, this once again lowers the bar for external contributors
who want to help the project, but would otherwise feel overwhelmed by
the rules we have to adhere to. (If we wouldn't have these rules, it would
be a lot harder for us to maintain a consistent and maintainable codebase).

The only interesting changes in this PR are those in `build.gradle`. All
other changes were auto-generated by running `./gradlew spotlessApply`.

Note that I disabled the formatting of Javadoc, as I think we should keep formatting
that ourselves. We normally put a lot of time and effort in our Javadoc and changing
that all at once seems like the wrong decision at this point in time.

[1]: https://github.com/google/google-java-format