LibWeb: Use more precise font metrics when doing inline layout

We now position inline-level boxes based on ascent and descent metrics
from the font in use. This makes our basic text layouts look a lot more
like those produced by other browsers. :^)

I've tried to match the terminology used by the CSS Inline Layout spec.

This will regress Acid2 a little bit, and probably various other sites,
but on the whole it's the direction we should be heading, so let's go.

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp

@@ -274,7 +274,7 @@ void InlineFormattingContext::generate_line_boxes(LayoutMode layout_mode)
                 item.margin_start,
                 item.margin_end,
                 item.width,
-                text_node.computed_values().font_size());
+                text_node.line_height());
             break;
         }
         }