Do not pass ReactContext to getViewManagersMap (#44379)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/44379

A common pattern to implement `ViewManagerOnDemandReactPackage` is to use a `getViewManagersMap` helper. If we capture `ReactApplicationContext` there, we will indefinitely retain the the very first ReactApplicationContext, and break/leak across reloads. Instead we should pass the `ReactApplicationContext` whenever we construct the ViewManager.

Changelog: [Internal]

Reviewed By: RSNara

Differential Revision: D56838427

fbshipit-source-id: 76583dd7f5564ed29f0dbfcef33d8d288cbb90e0