feat: Add ConnectionListener and a default browser implementation

[imownbey]

Motivation

online & offline support was disabled in React Native.

Solution

Added a ConnectionListener which is now used by PollingSubscriptions that defaults to a browser implementation. Default implementation should be safe to run in non-browser environments, defaulting to previous behavior of just always saying things are online.

Open questions

[ntucker]

Thanks for this great PR!

Unfortunately, branches not on this particular codebase don't get coverage automatically run. Can you run yarn test:coverage and paste results?

[imownbey]

-------------------------------------------|---------|----------|---------|---------|-------------------

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	99.58	97.64	98.52	99.56
legacy/src	100	100	100	100
index.ts	100	100	100	100
normalizr/src	100	100	100	100
denormalize.js	100	100	100	100
index.js	0	0	0	0
normalize.js	100	100	100	100
normalizr/src/schemas	100	99.12	100	100
Array.js	100	100	100	100
Entity.js	100	96.77	100	100	4
ImmutableUtils.js	100	100	100	100
Object.js	100	100	100	100
Polymorphic.js	100	100	100	100
Union.js	100	100	100	100
Values.js	100	100	100	100
rest-hooks/src	100	83.33	100	100
actionTypes.ts	100	100	100	100
errors.ts	0	0	0	0
index.ts	100	83.33	100	100	52
rest-hooks/src/react-integration	100	91.67	100	100
NetworkErrorBoundary.tsx	100	100	100	100
context.ts	100	100	100	100
index.ts	100	83.33	100	100	5
rest-hooks/src/react-integration/hooks	100	100	100	100
hasUsableData.ts	100	100	100	100
index.ts	100	100	100	100
useCache.ts	100	100	100	100
useError.ts	100	100	100	100
useFetcher.ts	100	100	100	100
useInvalidator.ts	100	100	100	100
useMeta.ts	100	100	100	100
useResetter.ts	100	100	100	100
useResource.ts	100	100	100	100
useRetrieve.ts	100	100	100	100
useSubscription.ts	100	100	100	100
rest-hooks/src/react-integration/provider	100	100	100	100
CacheProvider.tsx	100	100	100	100
ExternalCacheProvider.tsx	100	100	100	100
PromiseifyMiddleware.ts	100	100	100	100
index.ts	100	100	100	100
rest-hooks/src/resource	98.45	94.23	96.55	98.41
Entity.ts	92	83.33	77.78	92	19,89
Resource.ts	100	100	100	100
SimpleRecord.ts	100	100	100	100
SimpleResource.ts	100	100	100	100
index.ts	100	83.33	100	100	9
normal.ts	100	100	100	100
paramsToString.ts	100	100	100	100
types.ts	100	100	100	100
rest-hooks/src/state	99.07	94.39	96.23	99.02
BrowserConnectionListener.ts	80	100	80	80	9
NetworkManager.ts	100	95.45	100	100	129
PollingSubscription.ts	98.41	93.75	90.91	98.36	150
RIC.ts	100	100	100	100
SubscriptionManager.ts	100	87.5	100	100	79,104
actionCreators.ts	100	100	100	100
applyUpdatersToResults.ts	100	100	100	100
reducer.ts	100	95.24	100	100	34
rest-hooks/src/state/merge	100	100	100	100
isMergeable.ts	100	100	100	100
mergeDeepCopy.ts	100	100	100	100
rest-hooks/src/state/selectors	100	100	100	100
buildInferredResults.ts	100	100	100	100
getEntityPath.ts	100	100	100	100
index.ts	100	100	100	100
useDenormalized.ts	100	100	100	100
use-enhanced-reducer/src	100	100	100	100
index.ts	100	100	100	100
useEnhancedReducer.ts	100	100	100	100
usePromisifiedDispatch.ts	100	100	100	100
-------------------------------------------	---------	----------	---------	---------	-------------------

Test Suites: 28 passed, 28 total
Tests: 37 skipped, 342 passed, 379 total
Snapshots: 195 passed, 195 total
Time: 15.708s
Ran all test suites.
✨ Done in 21.85s.

[ntucker]

Hmm, doesn't this.run() still need to happen?

[imownbey]

It happens now by calling this.onlineListener() if we are online on line 43