Auto merge of #19350 - gterzian:ignore_aborted_responses_in_caching, r=jdm

Ignore aborted responses in caching

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@jdm @KiChjang @Manishearth Follow up on https://github.com/servo/servo/pull/18676 and https://github.com/servo/servo/pull/19274 to ignore aborted responses in caching.

I also found out the cache shouldn't return any response whose body is still in `ResponseBody::Receiving` mode, because that fails the assertion at https://github.com/servo/servo/blob/master/components/net/fetch/methods.rs#L438(we might want to add a channel as pat of the cached response later on to deal with this case). I only found out now because I needed the response from the server to trickle in so that it could be cached and aborted.

I copied the `http-cache.py` server from the wpt folder, and added a 'trickle' option, which is necessary to actually have a failing test with a cached but aborted request, it's now passing.

I also remove one unused import that slippled through previously.

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -12478,6 +12478,11 @@
      {}
     ]
    ],
+   "mozilla/resources/http-cache-trickle.py": [
+    [
+     {}
+    ]
+   ],
    "mozilla/resources/http-cache.js": [
     [
      {}
@@ -33251,6 +33256,12 @@
      {}
     ]
    ],
+   "mozilla/http-cache-xhr.html": [
+    [
+     "/_mozilla/mozilla/http-cache-xhr.html",
+     {}
+    ]
+   ],
    "mozilla/http-cache.html": [
     [
      "/_mozilla/mozilla/http-cache.html",
@@ -66358,6 +66369,10 @@
    "592f69ee432ba5bc7a2f2649e72e083d21393496",
    "testharness"
   ],
+  "mozilla/http-cache-xhr.html": [
+   "d4747fdc9ec6acc50718c13a668451987a44d219",
+   "testharness"
+  ],
   "mozilla/http-cache.html": [
    "33827dc9bdb0efcbcae4f730086693be315cfc14",
    "testharness"
@@ -72034,8 +72049,12 @@
    "78686147f85e4146e7fc58c1f67a613f65b099a2",
    "support"
   ],
+  "mozilla/resources/http-cache-trickle.py": [
+   "48f4e32ec2e1c1b6d47e89254045b398c1d84d40",
+   "support"
+  ],
   "mozilla/resources/http-cache.js": [
-   "c6b1ee9def26d4e12a1b93e551c225f82b4717c2",
+   "4bf71e1f328e778990eb756741a3be58f4f57ef6",
    "support"
   ],
   "mozilla/resources/iframe_contentDocument_inner.html": [