refactor: detect fabric with RN$Bridgeless

[tjzel]

Description

Since 0.74 RN$Bridgeless is always defined in the global object and bridgeless mode isn't supported anymore. Therefore checking RN$Bridgeless for Fabric is safer than depending on _IS_FABRIC variable which we intend to remove in the future. RN$Bridgeless is added to global much faster than _IS_FABRIC.

See software-mansion/react-native-reanimated#7043

Changes

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Screenshots / GIFs

Test code and steps to reproduce

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Checklist

• Included code example that can be used to test this change
• Updated TS types
• Updated documentation:
  • https://github.com/software-mansion/react-native-screens/blob/main/guides/GUIDE_FOR_LIBRARY_AUTHORS.md
  • https://github.com/software-mansion/react-native-screens/blob/main/native-stack/README.md
  • https://github.com/software-mansion/react-native-screens/blob/main/src/types.tsx
  • https://github.com/software-mansion/react-native-screens/blob/main/src/native-stack/types.tsx
• Ensured that CI passes

[kkafar]

Thanks!

The CI errors are unrelated.