Add Galley::intrinsic_size and use it in AtomLayout (#7146)

- part of https://github.com/emilk/egui/issues/5762
- also allows me to simplify sizing logic in egui_flex

crates/epaint/src/shapes/text_shape.rs

@@ -130,10 +130,12 @@ impl TextShape {
             num_vertices: _,
             num_indices: _,
             pixels_per_point: _,
+            intrinsic_size,
         } = Arc::make_mut(galley);
 
         *rect = transform.scaling * *rect;
         *mesh_bounds = transform.scaling * *mesh_bounds;
+        *intrinsic_size = transform.scaling * *intrinsic_size;
 
         for text::PlacedRow { pos, row } in rows {
             *pos *= transform.scaling;