Cleanup Network Handling in Gatherers

[patrickhulce]

Summary
The root cause of #11450 was that we link up network records and image elements using record.url === image.src but this breaks down for images that redirected. I looked around and it seems like many, many audits might be susceptible to a similar pitfall.

A few more things that came to mind we should probably fix in this space...

• Extract a shared findMatchingNetworkRecord function that can handle this redirect logic, do the *ByUrl nonsense that we have duplicated everywhere, etc
• Remove duplicated resourceSize in ImageElements that duplicates network record property (breaking change, ref ☂️ 👣 Breaking changes for v7 #11207)
• Check the redirect URL reporting behavior of...
  • ScriptElements
  • CSSUsage
  • JsUsage

i.e. when we create our map of URL -> network record we shouldn't just use URL, but also use..

// Also index all of its redirect source.
let originalRequest = record;
while (originalRequest.redirectSource) originalRequest = originalRequest.redirectSource;
map[originalRequest.url] = record;