Correctly represent connectivity

[Gudahtt]

According to EIP-1193 (permalink), the provider is "connected" when it can "service RPC requests to at least one chain". Currently the inpage provider doesn't make much of an attempt to guarantee this. Instead, 'connectivity' effectively represents whether or not the stream between the provider and MetaMask is active.

Certainly if the provider can't communicate with MetaMask, it can't service RPC requests either. But there remain many cases when the stream is live and the provider is "connected" but servicing RPC requests is impossible (e.g. when MetaMask is in the process of connecting to a network).