refactor(ios): open class feature switch for hermes

[wwwcg]

Before submitting a new pull request, please make sure:

• Test cases have been added/updated/passed for the code you will submit.
• Documentation has added or updated.
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• Squash the repeat code commits, short patches are welcome.

[hippy-service]

Hi, @wwwcg. Thanks for your PR! 👏

🏷️ You can leave a comment in this PR with #help tag when you need help (e.g. some status checks run failed due to internal issue), admin team members will help asap.