jest: Add jest-expo preset, to be used in the next commit.

A bit frustratingly, we need to install react-native-web, because
it's a peer dep of jest-expo, and react-dom, because that's a peer
dep of react-native-web.

It's likely that we'll never run any code in either module, since we
don't care about the web. (Expo seems to be expanding React Native's
original claim for multi-platform compatibility, namely iOS and
Android, to include the web. `react-native-web` looks like a thing
that lets you write React Native...for the web.)

At least they don't complain if we add them as dev dependencies
instead of regular dependencies.

Also, run `yarn yarn-deduplicate && yarn` as prompted by
`tools/test deps`.

package.json

@@ -116,6 +116,7 @@
     "jest-cli": "^24.9.0",
     "jest-environment-jsdom": "^24.9.0",
     "jest-environment-jsdom-global": "^1.2.0",
+    "jest-expo": "^37.0.0",
     "jest-extended": "^0.11.2",
     "jetifier": "^1.6.5",
     "lolex": "^5.1.1",
@@ -124,7 +125,9 @@
     "prettier-eslint": "^9.0.0",
     "prettier-eslint-cli": "^5.0.0",
     "prop-types": "^15.7.2",
+    "react-dom": "16.9.0",
     "react-native-cli": "^2.0.1",
+    "react-native-web": "^0.13.3",
     "redux-mock-store": "^1.5.1",
     "rollup": "^1.23.1",
     "rollup-plugin-babel": "^4.3.3",