layout: Avoid setting baseline for phantom line boxes (#39055)

Phantom line boxes should be treated as non-existing for most purposes,
so don't let them affect the baseline of their block container.

Testing: An existing test passes, and also adding a new one which
doesn't rely on `<button>`

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

tests/wpt/meta/MANIFEST.json

@@ -118868,6 +118868,19 @@
         {}
        ]
       ],
+      "inline-block-baseline-015.html": [
+       "34b4de90b5432c058c25f54927799ac687d95abd",
+       [
+        null,
+        [
+         [
+          "/css/reference/ref-filled-green-200px-square.html",
+          "=="
+         ]
+        ],
+        {}
+       ]
+      ],
       "line-height-201.html": [
        "00ab2aa52755d27c5bbd3b41d91a6f8e138c2899",
        [