Allow styling the cursor in MouseEventHandler

Co-Authored-By: Max Brunsfeld <max@zed.dev>
Co-Authored-By: Nathan Sobo <nathan@zed.dev>

gpui/src/platform.rs

@@ -47,6 +47,8 @@ pub trait Platform: Send + Sync {
 
     fn write_credentials(&self, url: &str, username: &str, password: &[u8]);
     fn read_credentials(&self, url: &str) -> Option<(String, Vec<u8>)>;
+
+    fn set_cursor_style(&self, style: CursorStyle);
 }
 
 pub(crate) trait ForegroundPlatform {
@@ -114,6 +116,13 @@ pub enum PromptLevel {
     Critical,
 }
 
+#[derive(Copy, Clone, Debug)]
+pub enum CursorStyle {
+    Arrow,
+    ResizeLeftRight,
+    PointingHand,
+}
+
 pub trait FontSystem: Send + Sync {
     fn load_family(&self, name: &str) -> anyhow::Result<Vec<FontId>>;
     fn select_font(