Issue 8000: Fix some problems with useBeanValidation

[UnklePig]

PR checklist

• [x] Read the contribution guidelines.
• [x] 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\.
• [x] Filed the PR against the correct branch: 3.0.0 branch for changes related to OpenAPI spec 3.0. Default: master.
• [x] Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

The useBeanValidation was not being set correctly in certain instances. In particular, when the default was set to true, in several languages it was impossible to set it to false. In addition, in all cases, the help message was always saying the default was false, even when it was actually true - which was pretty confusing. I have updated the cliOption so the default is set to "true" when appropriate. I have also modified the code for the languages that were failing so that setting the value to false is handled correctly for all languages.