Add epaint::Brush for controlling RectShape texturing (#5565)

Also wraps `Shape::Mesh` in an `Arc`.

No new features, but decreases size of `Shape` from 72 bytes to 64.

crates/epaint/src/tessellator.rs

@@ -1406,7 +1406,7 @@ impl Tessellator {
                     return;
                 }
 
-                out.append(mesh);
+                out.append_ref(&mesh);
             }
             Shape::LineSegment { points, stroke } => {
                 self.tessellate_line_segment(points, stroke, out);
@@ -1693,14 +1693,14 @@ impl Tessellator {
     /// * `rect`: the rectangle to tessellate.
     /// * `out`: triangles are appended to this.
     pub fn tessellate_rect(&mut self, rect: &RectShape, out: &mut Mesh) {
+        let brush = rect.brush.as_ref();
         let RectShape {
             mut rect,
             mut rounding,
             fill,
             stroke,
             mut blur_width,
-            fill_texture_id,
-            uv,
+            ..
         } = *rect;
 
         if self.options.coarse_tessellation_culling
@@ -1775,7 +1775,11 @@ impl Tessellator {
             path.add_line_loop(&self.scratchpad_points);
             let path_stroke = PathStroke::from(stroke).outside();
 
-            if uv.is_positive() {
+            if let Some(brush) = brush {
+                let crate::Brush {
+                    fill_texture_id,
+                    uv,
+                } = **brush;
                 // Textured
                 let uv_from_pos = |p: Pos2| {
                     pos2(
@@ -2173,7 +2177,7 @@ impl Tessellator {
 
         profiling::scope!("distribute results", tessellated.len().to_string());
         for (index, mesh) in tessellated {
-            shapes[index].shape = Shape::Mesh(mesh);
+            shapes[index].shape = Shape::Mesh(mesh.into());
         }
     }