[CORE]: replace deprecated methods

[codymikol]

replace setConfig and setOpenApi with the
non-deprecated config / openAPI methods

Fixes N/A

Replace usages of setOpenAPI and setConfig with non-deprecated usages config / openAPI.

There also seem to be a bunch of unused deprecated methods in this package. Are these used by some third party or can these be pruned if unused?

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.
• If contributing template-only or documentation-only changes which will change sample output, build the project beforehand.
• Run the shell script ./bin/generate-samples.shto update all Petstore samples related to your fix. 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*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

[wing328]

cc @OpenAPITools/generator-core-team

[jimschubert]

I think now is the time to make the change for these methods. We were stuck with them before 5.0 due to our rule about breaking changes.

Regarding unused methods, are you seeing methods in static analysis which are unused? If so, can you provide more details? We have a lot of SuppressWarnings with unused, but for the most part those are for tests, CLI options, and any place where reflection might be used in a way that IDEs don't know things are used when they are.