This saves time in CI spent performing the same source-level checks in
every build job. Checkstyle, PMD, and Spotless are now run once in the
"Lint and Format" job.
The -PskipPMD flag was replaced with a -PskipJavaFormat flag that
disables Checkstyle, PMD, and Spotless.
Also update Checkstyle to 8.38.
Google changed their style guide from the last time we imported it. This PR brings in those naming changes. The change they made is allowing single letter member, parameter, and local variable names. They also added a lambda naming scheme and I thought it would be good to bring that in too.
