Create @sentry/react-native/expo for simple plugin import

[krystofwoldrich]

• After add Expo config plugin #3391

Add cleaner Expo Plugin import.

Current:

app.config.js

const { withSentry } = require('@sentry/react-native/plugin/build/withSentry');
const config = {name: 'my app',};
module.exports = withSentry(config, {...});

Future:

app.config.js

const { withSentry } = require('@sentry/react-native/expo');
const config = {name: 'my app',};
module.exports = withSentry(config, {...});

[krystofwoldrich]

Done by #3429