Error Prone 2.19.0

New Checkers:

• NotJavadoc
• StringCaseLocaleUsage
• UnnecessaryTestMethodPrefix

Fixes issues: #956, #3504, #3654, #3703, #3731, #3737, #3760, #3779, #3796, #3809, #3813

Full Changelog: v2.18.0...v2.19.0