Fix React Native's React Navigation instrumentation examples

[jennmueng]

We need to change the example so users register the navigation container inside the onReady prop. React Navigation V5 does not actually set the ref on mount if linking is enabled, will need to move the registerNavigationContainer call to onReady as per react-navigation/react-navigation#8445 (comment).

Also, the functional component examples should be using useRef and not createRef.

Location:
https://docs.sentry.io/platforms/react-native/performance/included-instrumentation/#react-navigation-v5

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[jennmueng]

Was merged here: #3224. Looks like I forgot to link this issue.