Add Pinch to Zoom

This isn't necessarily a "must have" but is "very good to have". I keep forgetting about it and then see a big 2-pager and realize I can't zoom it 😕

When zoomed, it must also be pannable. Perhaps require zooming out all the way to change pages? Or, a more advanced way, when one is panned all the way to one side and then pans some more, change pages.

Of course, we already have two interactions on the Page view, changing pages and the "hold" to see menu. The "hold" was meant to just be a single tap (hold is definitely unintuitive), but I couldn't get single tap plus paging to work simultaneously in the initial version. This might be a good time to fix that as well.

This might require adding manual interactions and `Animated` to work. In which case, we'd probably need to use `react-native-gesture-handler`'s [cross-handler interactions](https://kmagiera.github.io/react-native-gesture-handler/docs/interactions.html) to implement. I'm not sure if there are simpler, cross-platform components or libraries that handle all of these interactions for you.
- RN's ScrollView does have [min and max zoom](https://facebook.github.io/react-native/docs/scrollview#maximumzoomscale) built-in, but only for iOS...
- [`react-native-image-zoom`](https://github.com/ascoders/react-native-image-zoom) handles some of this, but seems to unmaintained
- same with [`react-native-photo-view`](https://github.com/alwx/react-native-photo-view)
- [`react-native-image-viewer`](https://github.com/ascoders/react-native-image-viewer) seems fairly maintained and handles more, but not sure if everything. It also depends on `image-zoom`, which doesn't seem to be maintained (same developer)
- [`react-native-gallery-swiper`](https://github.com/Luehang/react-native-gallery-swiper) seems _very_ close to optimal, but from the docs I'm not sure how to ensure it always starts fully zoomed out or how to choose swipe direction. Like `image-viewer` it also supports headers/footers so it has a lot of the functionality out-of-the-box (including parts I already implemented).
- [`react-native-image-view`](https://github.com/antonKalinin/react-native-image-view) seems to handle less than the above 2