Failure to fetch ConnectionToken on app init does not throw or surface error

[jdivock-stripe]

Steps to repro:

• turn off backend
• initialize app

I think we need error handling logic in

stripe-terminal-react-native/src/components/StripeTerminalProvider.tsx

Lines 62 to 66 in f5e55a9

	const tokenProviderHandler = useCallback(async () => {
	const connectionToken = await tokenProvider();
	setConnectionToken(connectionToken);
	}, [tokenProvider]);

Currently the app will continue to init and calls to discoverReaders() will execute but not update discoveredReaders, more concerning the error payload from discoverReaders does not populate when there's no connectionToken in use.

Also it looks like there's logic in the iOS app about using the correct key that's surpassed so looks like we want to make sure we're surfacing that as well (thanks @jil-stripe #76)

[jdivock-stripe]

Also of note that the invalid connection token appears to be cached, we should reset it internally when it fails so a new one can be fetched

[jdivock-stripe]

going to raise the priority on this one as it's a pretty frustrating failure mode. The SDK will continue to try to perform actions and often just silently fail if it cannot reach the backend or has an invalid connection token.

[jdivock-stripe]

I worry fundamentally about having fetchConnectionToken fire on app mount a this seems fairly unexpected and I'm unsure how we'd properly wire in error surfacing around this. Can we refactor the SDK to be explicitly initialized by the user so they can delay configuring it without having to guard against mounting anything nested in <StripeTerminal/>

cc @dhenry-stripe