Correct generation of additionalProperties Map for numerous Java libraries (issue #20139)

[DavidGrath]

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in Git BASH)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

@martin-mfg , please help review for Java

[DavidGrath]

I'll ignore that failure on Circle CI node1 from now on

[DavidGrath]

@martin-mfg , thank you for the approval. I checked and CI failed the last 2 times because of a HTTP 503 while the machine was fetching packages. Should I bother making another trigger commit?

[martin-mfg]

Should I bother making another trigger commit?

@DavidGrath No, I think that's not necessary. I reran the pipelines here and everything is green. Just give the project maintainer a bit more time to merge your PR. :)

However, you could change the PR title to something more meaningful.