LibWeb: Start working on supporting fixed table layouts

Sometimes people make tables with a specific width. In those cases,
we can't just use the auto-sizing algorithm, but instead have to
respect whatever width the content specifies.

This is a bit rickety right now, since we don't implement generation
of anonymous table boxes.

The basic mechanism here is that block layout (which table-cell uses)
now has a virtual way of asking for the width of the logical containing
block. This is necessary as table-row does not produce a block-level
element and so was previously unable to provide a containing block
width for table-cell layout.

If the table has a non-auto specified width, we now interpret that as
a request to use fixed table layout. This will evolve over time. :^)

Libraries/LibWeb/Layout/LayoutTableCell.cpp

@@ -26,6 +26,7 @@
 
 #include <LibWeb/DOM/Element.h>
 #include <LibWeb/Layout/LayoutTableCell.h>
+#include <LibWeb/Layout/LayoutTableRow.h>
 
 namespace Web {
 
@@ -44,4 +45,11 @@ size_t LayoutTableCell::colspan() const
     return to<Element>(*node()).attribute(HTML::AttributeNames::colspan).to_uint().value_or(1);
 }
 
+float LayoutTableCell::width_of_logical_containing_block() const
+{
+    if (auto* row = first_ancestor_of_type<LayoutTableRow>())
+        return row->width();
+    return 0;
+}
+
 }