layout: Fix table geometry when collapsed borders have different sizes (#35122)

Even though when painting the collapsed borders we were using the right
size, when sizing the table we were treating cells as having a border
of half the maximum border size along the entire grid line.

Now we only take the maximum among the borders adjacent to the cell.

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

tests/wpt/meta/MANIFEST.json

@@ -105335,6 +105335,19 @@
         {}
        ]
       ],
+      "border-collapse-006.html": [
+       "f96c40cf95075703a67e9b13ef5b6f9e4e663ff8",
+       [
+        null,
+        [
+         [
+          "/css/reference/ref-filled-green-200px-square.html",
+          "=="
+         ]
+        ],
+        {}
+       ]
+      ],
       "border-collapse-applies-to-016.xht": [
        "f102d6a799b195388f57396024532947e3357303",
        [