restructured language directory to one directory per language

[Fjolnir-Dvorak]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Tracking Pull request for the refactoring of the language directory to one directory per language.
Referring ticket #1893 ([REQ] Code Refactoring: strucuring modules/openapi-generator/src/main/java/org/openapitools/codegen/languages into one package per language)

[jimschubert]

Thanks for this PR. I'm concerned that this introduces the language-as-a-toplevel generator construct that we've been getting away from since the start of this fork. And this change will directly conflict with the refactoring design put forth here: https://github.com/OpenAPITools/openapi-generator/projects/5

[Fjolnir-Dvorak]

Ok. That was just the first thing that came to my mind to try to help you to improve the maintainability, readablily and the modularity of the project.

[jimschubert]

@Fjolnir-Dvorak I'd be interested in your feedback regarding the approach I've proposed in #842.

[jimschubert]

Also, for reference of the refactor which I had mentioned, see #845

[wing328]

@Fjolnir-Dvorak thanks for the PR but at this stage we'll proceed further with this change based on the reasons provided by @jimschubert