[snackager] Add explicit RN web external for react native maps

[byCedric]

Why

Currently, bundling of react-native-maps@0.29.4 fails with the error:

Failed to resolve dependency 'react-native-maps@0.29.4' (Module not found: Error: Package path ./unstable-native-dependencies is not exported from package /tmp/snackager/snackager/buildStatus/1/react-native-maps@0.29.4-ios,android,web/package/node_modules/react-dom (see exports field in /tmp/snackager/snackager/buildStatus/1/react-native-maps@0.29.4-ios,android,web/package/node_modules/react-dom/package.json)
Retry
Module not found: Error: Package path ./unstable-native-dependencies is not exported from package /tmp/snackager/snackager/buildStatus/1/react-native-maps@0.29.4-ios,android,web/package/node_modules/react-dom (see exports field in /tmp/snackager/snackager/buildStatus/1/react-native-maps@0.29.4-ios,android,web/package/node_modules/react-dom/package.json))

In this run you can see that react-dom and react-native-web are getting sucked into the bundle.

How

• Added explicit RN web external to avoid react-dom getting sucked into the bundle.

Test Plan

• See if bundling passes with this change

[byCedric]

Yep, that worked! https://github.com/expo/snack/runs/6306510939?check_suite_focus=true#step:6:209