[native] Change ChatContextProvider position

Summary:
This diff changes position of ChatContextProvider. It is necessary, because we use useNavigation hook in markdown-chat-mention.react.js and when we render dummy nodes (which are needed for our virtualised list) we don't have access to NavigationContainer.

Depends on D8846.

Test Plan:
Tested if ChatContextProvider is used in:

• MessageSearchProvider
• RegistrationContextProvider
• SQLiteDataHandler
• ConnectedStatusBar
• ReduxPersistGate
• gated:
  • LifecycleHandler
  • DisconnectedBarVisibilityHandler
  • DimensionsUpdater
  • ConnectivityUpdater
  • ThemeHandler
  • OrientationHandler
• PersistedStateGate
• Socket

and it is not. Also checked locations where we use ChatContext:

• native/chat/message-list-container.react.js
• native/chat/message-list-types.js
• native/chat/message-results-sceen.react.js
• native/chat/multimedia/robotext/text-message.react.js
• native/chat/sidebar-navigation.js
• native/search/message-search.react.js
• native/tooltip/tooltip.react.js

All of these files are "inside" RootNavigator. Only chatMessageItemKey from native/chat/utils.js is used in chat-item-height-measurer.react.js but this file is used in chat-context-provider.react.js only.

Reviewers: tomek, inka

Reviewed By: tomek, inka

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8847