layout: Reverse vertical orientation of gradients using corner directions. (#37802)

Found and manually tested by comparing rendering between Firefox and
Servo.

Testing: Existing WPT coverage is sufficient.
Fixes: #37782

Signed-off-by: Josh Matthews <josh@joshmatthews.net>

tests/wpt/meta/MANIFEST.json

@@ -204735,6 +204735,19 @@
        {}
       ]
      ],
+     "linear-gradient-non-square.html": [
+      "2b4f48990f24bd74ec638d39a5f569f56cb63664",
+      [
+       null,
+       [
+        [
+         "/css/css-images/reference/linear-gradient-non-square-ref.html",
+         "=="
+        ]
+       ],
+       {}
+      ]
+     ],
      "linear-gradient-sibling-index.html": [
       "b92897e0697441df6876b88e53daa148a5edb009",
       [
@@ -440282,6 +440295,10 @@
       "200x200-blue-black-green-red.html": [
        "04322b066c316b8b89c73d966e00f607447edd8e",
        []
+      ],
+      "linear-gradient-non-square-ref.html": [
+       "1ad3c75747e05768a3e79d879e535e8b3980f1a4",
+       []
       ]
      },
      "repeating-conic-gradient-ref.html": [