[swift5][client] Fix module and class with same name

Created by: 4brunu

It fixes https://github.com/OpenAPITools/openapi-generator/issues/9953

With https://github.com/OpenAPITools/openapi-generator/pull/9624 we changed a class from #projectName#API to #projectName#.

But it seems that the Swift compiler had a bug related to projects that have a class with the same name of the module.

More details on this https://github.com/OpenAPITools/openapi-generator/issues/9953 and https://bugs.swift.org/browse/SR-898.

This PR reverts the change from #projectName#API to #projectName#, but keeps the reference to a warning to help with the transition. Once the transition is made, this warning can be removed with the new introduced flag removeMigrationProjectNameClass.

@aymanbagabas do you have other suggestions to fix this issue?

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