linux: Primary clipboard (#10534)

Implements copying from and pasting to the primary selection.

Release Notes:

- N/A

crates/gpui/src/platform/windows/platform.rs

@@ -692,6 +692,8 @@ impl Platform for WindowsPlatform {
         false
     }
 
+    fn write_to_primary(&self, _item: ClipboardItem) {}
+
     fn write_to_clipboard(&self, item: ClipboardItem) {
         if item.text.len() > 0 {
             let mut ctx = ClipboardContext::new().unwrap();
@@ -699,6 +701,10 @@ impl Platform for WindowsPlatform {
         }
     }
 
+    fn read_from_primary(&self) -> Option<ClipboardItem> {
+        None
+    }
+
     fn read_from_clipboard(&self) -> Option<ClipboardItem> {
         let mut ctx = ClipboardContext::new().unwrap();
         let content = ctx.get_contents().unwrap();