Checkstyle 8.26

[Roman Ivanov]

Checkstyle 8.26 - https://checkstyle.org/releasenotes.html#Release_8.26

Breaking backward compatibility:

  Remove AbstractTypeAwareCheck and combine the missing pieces into JavadocMethod

  remove functionality of Checker.setClassLoader and TreeWalker.setClassLoader

Bug fixes:

  WriteTag: Add localization for javadoc.write.tag message

Notes:

  upgrade to pmd 6.18.0

  Tests fail on OpenJDK 12 due to 'Failed to find the "modifiers" field in method setInternalState.'

  Purpose of UnnecessarySemicolonAfterTypeMemberDeclaration is unclear in documentation.

  doc: fix config sample for SuppressWithNearbyCommentFilter

  config: fix Travis items to do more jdk11 and jdk12 builds

  Align XDocs and Javadocs for modifiers package

  Align XDocs and Javadocs for header package

  Align XDocs and Javadocs for regexp package

   Align XDocs and Javadocs for metrics package

   Align XDocs and Javadocs for imports package

  create examples for UnnecessaryParentheses usage 

  Fix JitCI build

  Review disabled validations of eclipse compiler

  config: fix previous commits check to avoid confusion with master and rewrite main ci for easier maintenance

  Use ja-JP for Japanese locale, zh-CN for Chinese locale in travis.sh

  Pitest: add new mutator REMOVE_CONDITIONALS

  Remove usage of DetailAST.branchContains

  Fix pitest coverage for RightCurly

  spotbugs is not executed in build process of openjdk12