Auto merge of #18676 - gterzian:continue_http_cache_work, r=jdm

Continue http cache work

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Work in progress, and not quite worth a review yet. (Continuation of https://github.com/servo/servo/pull/4117)

TODO

- [ ] cache metadata (find some subset of`net_traits::Metadata` that can be shared across threads, it seems the problem is mainly stuff inside `hyper::header` in the `headers` field)

- [ ] determine which other fields of a `Response` need to be cached, so a full and valid one can be returned upon a cache hit.

- [ ] determine how to best share the cache across fetch threads (inside HttpState like I tried now?)

- [ ] Spend more time reading the spec and make sure the cache follows it where it matters.

- [ ] Make the current wpt tests pass.

- [ ] More...

---
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #12972  (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -12466,6 +12466,11 @@
      {}
     ]
    ],
+   "mozilla/resources/http-cache.js": [
+    [
+     {}
+    ]
+   ],
    "mozilla/resources/iframe_contentDocument_inner.html": [
     [
      {}
@@ -33218,6 +33223,12 @@
      {}
     ]
    ],
+   "mozilla/http-cache.html": [
+    [
+     "/_mozilla/mozilla/http-cache.html",
+     {}
+    ]
+   ],
    "mozilla/iframe-unblock-onload.html": [
     [
      "/_mozilla/mozilla/iframe-unblock-onload.html",
@@ -66309,6 +66320,10 @@
    "592f69ee432ba5bc7a2f2649e72e083d21393496",
    "testharness"
   ],
+  "mozilla/http-cache.html": [
+   "33827dc9bdb0efcbcae4f730086693be315cfc14",
+   "testharness"
+  ],
   "mozilla/iframe-unblock-onload.html": [
    "8734756947d36b047df256f27adc56fce7e31f88",
    "testharness"
@@ -71981,6 +71996,10 @@
    "78686147f85e4146e7fc58c1f67a613f65b099a2",
    "support"
   ],
+  "mozilla/resources/http-cache.js": [
+   "c6b1ee9def26d4e12a1b93e551c225f82b4717c2",
+   "support"
+  ],
   "mozilla/resources/iframe_contentDocument_inner.html": [
    "eb1b1ae3bb7a437fc4fbdd1f537881890fe6347c",
    "support"