layout: Add line height from preserved segment breaks in quirks mode (#31419)

In quirks mode, preserved segment breaks should add line height to
lines. This matches the behavior of WebKit and Blink, but not Gecko.

This also handles the special-case of `<br>` elements, which are
implemented with preserved segment breaks via `white-space: pre-line`.
This is an implementation detail though because `<br>` has a special
behavior if the line isn't empty -- it doesn't add any line height in
this case.

tests/wpt/mozilla/meta/MANIFEST.json

@@ -5402,6 +5402,19 @@
       {}
      ]
     ],
+    "quirks-mode-br-line-height.html": [
+     "ecb49833f809e72cd57772e7a98085e787cb8baa",
+     [
+      null,
+      [
+       [
+        "/_mozilla/css/quirks-mode-br-line-height-ref.html",
+        "=="
+       ]
+      ],
+      {}
+     ]
+    ],
     "quotes_none_a.html": [
      "c37ff23e9084d7d198b3c97e14d2e00ab417dd6c",
      [
@@ -9673,6 +9686,10 @@
      "0195f154cf3c4303e5aaf4fc9e7cfa358b8386d7",
      []
     ],
+    "quirks-mode-br-line-height-ref.html": [
+     "2108a4ae5e1f823cf2a3923070d54c42487fd8c6",
+     []
+    ],
     "quotes_none_ref.html": [
      "85f3cf14ca2da71a45efd75803e84e7b5dc23a85",
      []