chore: support RCT_USE_RN_DEP and RCT_USE_PREBUILT_RNCORE flags

[thymikee]

Summary

Since running pod install is deprecated in favor of running npm run ios command, I'm adding a way to support RN prebuilds available in 0.80 and 0.81:

Test Plan

Example usage:

RCT_USE_RN_DEP=1 RCT_USE_PREBUILT_RNCORE=1 npm run ios

Checklist

• Documentation is up to date.
• Follows commit message convention described in CONTRIBUTING.md.
• For functional changes, my test plan has linked these CLI changes into a local react-native checkout (instructions).