core(network-request): identify filesystem resources as non-network

[patrickhulce]

Summary
Closes three holes in our isNonNetworkRequest logic:

1. file protocol URLs were considered network requests.
2. filesystem protocol URLs were considered network requests. (it's different!)
3. When requests are blocked or otherwise don't receive a response the protocol field is left empty and requests weren't identified as non-network.

Related Issues/PRs
fixes #12915

[connorjclark]

what about filesystem? https://github.com/GoogleChrome/lighthouse/pull/12920/files#diff-2302fa8968cce5aae24372b1b88c1e2927f40626f261646064b57d4434840066R23

[patrickhulce]

@connorjclark in practice I was never able to observe filesystem actually be populated in these cases were you?

All file: URLs were blocked immediately in my tests which triggers the empty protocol branch. EDIT: filesystem is completely different from file got it 👍

We definitely have a larger issue lurking here with protocol and scheme being used interchangeably throughout the codebase even though they can be quite different (h2 vs. https). I'll file an issue for that 👍