1650747 - Investigate removing `files` Map from HarCollector

Status: NEW

(DevTools :: Netmonitor, task, P3)

Description

[Alexandre Poirot [:ochameau]]

This Map looks redundant with the cached resources already done from the ResourceWatcher:
https://searchfox.org/mozilla-central/rev/c86c19bd64f8f19590a4190c282781d3a9631422/devtools/client/netmonitor/src/har/har-collector.js#186-195
We store the resource "onNetworkEvent", which is equivalent to onResourceAvailable,
and then from "onNetworkEventUpdate", which is equivalent to onResourceUpdate, we retrieve the cached resource:
https://searchfox.org/mozilla-central/rev/c86c19bd64f8f19590a4190c282781d3a9631422/devtools/client/netmonitor/src/har/har-collector.js#204-208
On top of that, we are using packet.from or resource.actor which is a low level detail we shouldn't be using in the frontend.

Doing such cleanup would probably help implementing server side network e
vent resources, bug 1644191.