Using @objcMembers to expose all props and funcs to ObjC

[tsanidas]

When using the objcCompatible option for swift5, this will add @objcMembers instead of @objc at the generated class level for Models and APIs so that all properties and functions will be visible by Objective-C. I had suggested this in issue 13175 as an enhancement.
I've re-generated the samples, which now reflect this change, and there are no changes to docs.

Attn: @jgavris @ehyche @Edubits @jaz-ah @4brunu

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[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[tsanidas]

@wing328 Ok, I hope that fixed it. Incorrectly juggled work email with GitHub email.

[4brunu]

Looks good, thanks for creating this PR 👍