Add android expo support and permissions checker

[jdivock-stripe]

Summary

This one wound up being an adventure, here are the hits:

• built another permissions util specific to expo / android, it makes use of the react-native-permissions lib which is not compatible with react-cli and our example app so it's been broken out.
• added target to the expo plugin to update the AndroidManifest.xml file with the required user-permissions to gain BT access an enable react-native-permissions to work
• added docs on all these special steps

That said, we should revisit all this when expo is updated to 45 as I imagine most of these rough edges will be handled.

Motivation

#201

Testing

Validated on my expo example app, works 🎉

• I tested this manually
• I added automated tests

Documentation

Select one:

• I have added relevant documentation for my changes.
• This PR does not result in any developer-facing changes.

[dhenry-stripe]

Looks good!

[dhenry-stripe]

nit: can we deduplicate by linking to docs/set-up-your-sdk.md?

[jdivock-stripe]

yeah, I was thinking of making a partial. I believe the intent with everything in /docs is to eventually migrate it into our docs portal. Once we get that going we can gate in users and scrap just about everything in the README aside from our alpha/hero users steps

[dhenry-stripe]

This is a good starting point, but users will also need to detect whether a permission denial was temporary or permanent. Android permissions have three states:

• Granted
• Denied, which has two substates:
  • Denied once
  • Denied permanently (ie checking the "Never ask again" checkbox in the permission dialog UI)

If a permission is denied permanently then the permissions dialog is never displayed to the user and the permission request is automatically denied.

react-native-permissions seems to model the permanent denial using RESULTS.BLOCKED [0]. I suggest we consider exposing this (or some abstraction of it to hide the lib) to applications to allow them to appropriately handle the permanent denial case.

Or, failing that leave a comment to warn consumers that they'll need to implement permanent denial handling themselves.

[0] https://github.com/zoontek/react-native-permissions#android-flow

[jdivock-stripe]

Or, failing that leave a comment to warn consumers that they'll need to implement permanent denial handling themselves.

That would work, but honestly it feels like we can just return a typed error object here and let the user decide cause at that point their app is useless. I'm thinking something along the lines of:

type Error = { error: Record<string, string> | null };

and {error: null} if all perms are granted

[jdivock-stripe]

alright, gave it the ole refactor. I don't feel great about having 2 perms utils that are nearly identical, but hopefully the expo one can just go away in the next Expo release when they hopefully handle this better.

[arekkubaczkowski]

well done 👍