Move `useNativeInit` inside options

[antonis]

Move useNativeInit from a top-level Expo plugin prop into the options object in v9.

Currently:

["@sentry/react-native/expo", {
  "useNativeInit": true,
  "options": {
    "dsn": "https://key@sentry.io/123"
  }
}]

Proposed for v9:

["@sentry/react-native/expo", {
  "options": {
    "useNativeInit": true,
    "dsn": "https://key@sentry.io/123"
  }
}]

Context: #5804 (comment)

[linear-code]

RN-537