When developing in OAP (introducing new functionality/fixing bugs), it is tiresome to search for the relevant directories containing the templates for each generator. This PR introduces javadocs to all the codegens making the ńavigation to the templates directories much easier.

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 WSL)
  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 solves a reported issue, reference it using GitHub's linking syntax (e.g., having "fixes #123" present in the PR description)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request. - @wing328 - this is definitely just something nice-to-have. I find it very hard to find the directory containing the template files when I work in the codebase. But it is a matter of opinion definitely and maybe I am the only one with such issues and this should not be merged.

Summary by cubic

Added class-level Javadocs to all generators pointing to their template directories to make template discovery fast and consistent. For multi-library generators, docs list root vs libraries/ paths and note that library templates shadow root templates.

• Refactors
  • Added Javadoc in each *Codegen class with its src/main/resources/... template path(s).
  • Standardized wording, noted template engines where needed (e.g., Handlebars in gdscript), and moved annotations below Javadocs so the docs attach to the class.

^{Written for commit 489dff0. Summary will update on new commits.}