Fix #18715 ensure codegen fields and additionalProperties are not conflicting

Reduce the numbers of conflicting values between java code and mustache templating.

Only write back to additionalProperties if it was present -> this ensures that boolean are correctly converted -> this ensures that there is no mismatch. Do not writeBack to additionalProperties if not present (with a few exception for backward compatibility with unit tests). Use the field values as much as possible in the java code instead of additionalProperties. In mustache, use the additionalProperties as the primary context and the codegen instance in mustache as the parent context. So mustache retrieve the values in this order:

additionalProperty codegen.getter codegen.field

It greatly reduces the need to put values in additionalProperties. A field or a getter in codeGen can be used instead.

The changes impact mainly the DefaultCodeGen and the java generators. For the java generators, the generated output stays the same.

There can be side effects for other generators. For example scala now include the email in the generated modes. It seems that it was the initial intention. It is an example of the misunderstanding that this PR tries to solve. typescript now use the correct version in README.md elm now use the correct version in README.md ruby There were too many discrepencies between the fields and the additionalProperty. There is a fallback to the old behaviour

PR checklist

[x] Read the contribution guidelines.
[x] 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.
[x] Run the following to build the project and update samples:
```
./mvnw clean package 
./bin/generate-samples.sh ./bin/configs/*.yaml
./bin/utils/export_docs_generators.sh
```
(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.
[x] File the PR against the correct branch: master (upcoming 7.6.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
[x] If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

General commitee @wing328

Java commitee @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10) @martin-mfg (2023/08)

Scala commitee @clasnake (2017/07), @jimschubert (2017/09) ❤️, @shijinkui (2018/01), @ramzimaalej (2018/03), @chameleon82 (2020/03), @Bouillie (2020/04) @fish86 (2023/06)

OpenAPITools / openapi-generator

Fix #18715 ensure codegen fields and additionalProperties are not conflicting #18818

PR checklist