Separate WrappedLines from ShapedLines

ShapedLines are never wrapped, whereas WrappedLines are optionally wrapped if
they are associated with a wrap width. I tried to combine everything because
wrapping is inherently optional for the Text element, but we have a bunch of
APIs that don't make sense on a line that may wrap, so we need a distinct type
for that case.

crates/gpui2/src/style.rs

@@ -203,6 +203,7 @@ impl TextStyle {
                 style: self.font_style,
             },
             color: self.color,
+            background_color: None,
             underline: self.underline.clone(),
         }
     }