Use case sensitivity when checking reserved words

Created by: gbrown-ce

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\.
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Description of the PR

Open API generator previously wasn't case sensitive when checking for reserved words in the typescript generator. This will allow us to have the "Package" model in ProductCatalogs without needing to rename anything. Related issue: https://github.com/OpenAPITools/openapi-generator/issues/349

@TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny