Parent issue: #19604

Description

Add Checkstyle checks for all rules under §4.1 - Package Names of the OpenJDK Java Style Guidelines v6.

Rules covered

From §4.1 - Package Names:

1. Package names should be all lower case without underscores or other special characters.
2. Don’t use plural form. Follow the convention of the standard API which uses for instance java.lang.annotation and not java.lang.annotations. [Not coverable]

Checks to add to openjdk_checks.xml

TreeWalker-level:

<module name="PackageName">
  <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
</module>