Java (OpenJDK) using commonmark-java

Since this pull request, Java (OpenJDK) has included a copy of commonmark-java:

• https://github.com/openjdk/jdk/pull/16388

When they copied the source files, they made a few adjustments too. There's a list here:

// This module is primarily an import from a recent tagged version of
//     https://github.com/commonmark/commonmark-java
//
// The following parts are imported:
//
// * commonmark/src/main/java
// * commonmark/src/main/resources
// * commonmark-ext-gfm-tables/src/main/java
// * commonmark-ext-gfm-tables/src/main/resources
//
// For source and resource files, the following transformations are applied:
//
// * legal headers are added
// * package and import statements are updated
// * characters outside the ASCII range are converted to Unicode escapes
// * @SuppressWarnings("fallthrough") is added to getSetextHeadingLevel
// * the value for ENTITY_PATH is updated with the modified package
// * the file `entities.properties` is renamed to `entities.txt`

Let's make it easier for them next time by adopting some of the changes.

Start by comparing the commonmark/src/main/java and commonmark/src/main/resources paths, plus commonmark-ext-gfm-tables/src/main/java and src/main/resources, with the copied OpenJDK files referenced in module-info.java. Review each listed transformation and the related source and resource layout. Done means the relevant differences are addressed so a future OpenJDK import needs fewer adjustments.