port over stylistic cleanups from the panama-foreign repo.

The following PRs are included:

https://github.com/openjdk/panama-foreign/pull/863
https://github.com/openjdk/panama-foreign/pull/888
https://github.com/openjdk/panama-foreign/pull/889
https://github.com/openjdk/panama-foreign/pull/893
https://github.com/openjdk/panama-foreign/pull/894
https://github.com/openjdk/panama-foreign/pull/897
https://github.com/openjdk/panama-foreign/pull/906