Track percentage-based margins in UIHTMLWidget and re-resolve them when
the containing parent acquires its final size. This prevents margins
computed against an initial zero-width container from remaining stale
until the viewport is resized.
Add regressions covering percentage margin recomputation and the SS64
footer layout after a deferred stylesheet is loaded.
Reserve stylesheet source positions when link elements are encountered
instead of assigning them when asynchronous loading completes.
Track the stylesheet and rule ordinals explicitly so deferred external
styles retain their document order relative to later inline styles.
Preserve this ordering when extracting marked stylesheet rules.
Add an SS64 regression test covering heading and button styles after a
deferred stylesheet finishes loading.
