Implement underlining for IME areas (#284)

![image](https://github.com/linebender/xilem/assets/36049421/5378dc8c-bb2a-4dba-bbb1-352d827a617b)

crates/masonry/src/text2/edit.rs

@@ -71,7 +71,16 @@ impl<T: EditableText> TextEditor<T> {
 
     pub fn rebuild(&mut self, fcx: &mut FontContext) {
         // TODO: Add the pre-edit range as an underlined region in the text attributes
-        self.inner.rebuild(fcx);
+
+        self.inner.rebuild_with_attributes(fcx, |mut builder| {
+            if let Some(range) = self.preedit_range.as_ref() {
+                builder.push(
+                    &parley::style::StyleProperty::Underline(true),
+                    range.clone(),
+                );
+            }
+            builder
+        });
     }
 
     pub fn draw(&mut self, scene: &mut Scene, point: impl Into<Point>) {

crates/masonry/src/text2/selection.rs

@@ -7,6 +7,7 @@ use std::borrow::Cow;
 use std::ops::{Deref, DerefMut, Range};
 
 use kurbo::{Affine, Line, Point, Stroke};
+use parley::context::RangedBuilder;
 use parley::FontContext;
 use unicode_segmentation::{GraphemeCursor, UnicodeSegmentation};
 use vello::peniko::{Brush, Color};
@@ -210,28 +211,38 @@ impl<T: Selectable> TextWithSelection<T> {
         self.needs_selection_update = true;
     }
 
-    // Intentionally aliases the method on
-    pub fn rebuild(&mut self, fcx: &mut FontContext) {
+    // Intentionally aliases the method on `TextLayout`
+    pub fn rebuild_with_attributes(
+        &mut self,
+        fcx: &mut FontContext,
+        attributes: impl for<'b> FnOnce(
+            RangedBuilder<'b, TextBrush, &'b str>,
+        ) -> RangedBuilder<'b, TextBrush, &'b str>,
+    ) {
         // In theory, we could be clever here and only rebuild the layout if the
         // selected range was previously or currently non-zero size (i.e. there is a selected range)
         if self.needs_selection_update || self.layout.needs_rebuild() {
             self.layout.invalidate();
             self.layout.rebuild_with_attributes(fcx, |mut builder| {
                 if let Some(selection) = self.selection {
-                    let range = selection.min()..selection.max();
+                    let range = selection.range();
                     if !range.is_empty() {
                         builder.push(
                             &parley::style::StyleProperty::Brush(self.highlight_brush.clone()),
                             range,
                         );
                     }
                 }
-                builder
+                attributes(builder)
             });
             self.needs_selection_update = false;
         }
     }
 
+    pub fn rebuild(&mut self, fcx: &mut FontContext) {
+        self.rebuild_with_attributes(fcx, |builder| builder);
+    }
+
     pub fn draw(&mut self, scene: &mut Scene, point: impl Into<Point>) {
         // TODO: Calculate the location for this in layout lazily?
         if let Some(selection) = self.selection {