net: Perform CSP checks on fetch responses. (#37154)

Also add clarifying comments to the SRI WPT tests with
regards to the `www.` domain and how that interacts with
the integrity checks.

Lastly, adjust the casing for `Strict-Dynamic`, as in
the post-request check that should also be case-insensitive.

Closes servo/servo#37200
Closes servo/servo#36760
Fixes servo/servo#36499
Part of w3c/webappsec-csp#727
Fixes w3c/webappsec-csp#728
Part of servo/servo#4577

Signed-off-by: Josh Matthews <josh@joshmatthews.net>
Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>
Co-authored-by: Josh Matthews <josh@joshmatthews.net>

tests/wpt/meta/MANIFEST.json

@@ -397312,7 +397312,7 @@
       []
      ],
      "script-src-strict_dynamic_parser_inserted.html.headers": [
-      "b7918c93323eff9db66ad26a73b78798d35e5f7b",
+      "9d0b3b93d44db43be7d19c34483bc1e63ef777a0",
       []
      ],
      "script-src-strict_dynamic_parser_inserted_correct_nonce.html.headers": [
@@ -568648,7 +568648,7 @@
       ]
      ],
      "default-src-sri_hash.sub.html": [
-      "87fce5961fd1854303377ee939b21b6275b312cf",
+      "87389c306a53fdffa9806ba05f08a097713bcc37",
       [
        null,
        {}
@@ -573246,7 +573246,7 @@
       ]
      ],
      "script-src-sri_hash.sub.html": [
-      "9216e2b0d4971fc46d0010e8dfa7375845187a8d",
+      "e290911183d0b9a5dccf4a6a2eaa3b12ee25c682",
       [
        null,
        {}
@@ -573351,7 +573351,7 @@
       ]
      ],
      "script-src-strict_dynamic_parser_inserted.html": [
-      "c5e33dc4253dbf3ce2b0c6cb2fca4b0306d68244",
+      "9a8ad7a4ef2b5592af70d4dcc56f291e75da8e1b",
       [
        null,
        {}