Revert "Revert recent anti-aliasing improvements (#24289)" and fix selection top right corner radius issue (#24342)

Release Notes:

- N/A

----

To fix #24289 mention issue and revert PathBuilder and MSAA.

I'm sorry about of this, in #22808 I was forgotten this bit of detail.


![image](https://github.com/user-attachments/assets/112afda2-088c-41d0-83bd-808f6cd2f9d5)

So, add `move_to` here, we can fix the selection top right corner radius
issue.

## After change

<img width="1383" alt="image"
src="https://github.com/user-attachments/assets/28ea103c-d652-41d6-bbe0-7fd042d81e77"
/>

crates/gpui/src/scene.rs

@@ -715,6 +715,13 @@ impl Path<Pixels> {
         }
     }
 
+    /// Move the start, current point to the given point.
+    pub fn move_to(&mut self, to: Point<Pixels>) {
+        self.contour_count += 1;
+        self.start = to;
+        self.current = to;
+    }
+
     /// Draw a straight line from the current point to the given point.
     pub fn line_to(&mut self, to: Point<Pixels>) {
         self.contour_count += 1;
@@ -744,7 +751,8 @@ impl Path<Pixels> {
         self.current = to;
     }
 
-    fn push_triangle(
+    /// Push a triangle to the Path.
+    pub fn push_triangle(
         &mut self,
         xy: (Point<Pixels>, Point<Pixels>, Point<Pixels>),
         st: (Point<f32>, Point<f32>, Point<f32>),