layout: Share styles to inline box children via SharedInlineStyles (#36896)

`TextRun`s use their parent style to render. Previously, these styles
were cloned and stored directly in the box tree `TextRun` and resulting
`TextFragment`s. This presents a problem for incremental layout.
Wrapping the style in another layer of shared ownership and mutability
will allow updating all `TextFragment`s during repaint-only incremental
layout by simply updating the box tree styles of the original text
parents.

This adds a new set of borrows when accessing text styles, but also
makes it so that during box tree block construction
`InlineFormattingContext`s are created lazily and now
`InlineFormattingContextBuilder::finish` consumes the builder, making
the API make a bit more sense. This should also improve performance of
box tree block construction slightly.

Testing: This should not change observable behavior and thus is covered
by existing WPT tests.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>

tests/wpt/meta/MANIFEST.json

@@ -167223,6 +167223,19 @@
        {}
       ]
      ],
+     "display-contents-inline-002.html": [
+      "f40a34129f348aca37fca83f70598053cf22785b",
+      [
+       null,
+       [
+        [
+         "/css/css-display/display-contents-pass-no-red-ref.html",
+         "=="
+        ]
+       ],
+       {}
+      ]
+     ],
      "display-contents-inline-flex-001.html": [
       "43b502731aefbaa348671e32171f0e1eb4bca04b",
       [