gpui: Improve path rendering & global multisample anti-aliasing (#29718)

Currently, the rendering path required creating a texture for each path,
which wasted a large amount of video memory. In our application, simply
drawing some charts resulted in video memory usage as high as 5G.

I removed the step of creating path textures and directly drew the paths
on the rendering target, adding post-processing global multi-sampling
anti-aliasing. Drawing paths no longer requires allocating any
additional video memory and also improves the performance of path
rendering.

Release Notes:

- N/A

---------

Co-authored-by: Jason Lee <huacnlee@gmail.com>

crates/gpui/src/platform.rs

@@ -789,7 +789,6 @@ pub(crate) struct AtlasTextureId {
 pub(crate) enum AtlasTextureKind {
     Monochrome = 0,
     Polychrome = 1,
-    Path = 2,
 }
 
 #[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]