Fix multi-cursor copy/paste on linux (#13523)

The clipboard library we use for X11 doesn't yet support multiple
formats on the clipboard, so for now we just store this in memory for
the current zed process, as we do for Wayland.

Fixes: #11971

Release Notes:

- N/A

---------

Co-authored-by: Mikayla Maki <mikayla@zed.dev>

crates/gpui/src/platform/linux/x11/client.rs

@@ -29,9 +29,9 @@ use xkbcommon::xkb as xkbc;
 use crate::platform::linux::LinuxClient;
 use crate::platform::{LinuxCommon, PlatformWindow};
 use crate::{
-    modifiers_from_xinput_info, point, px, AnyWindowHandle, Bounds, CursorStyle, DisplayId,
-    Keystroke, Modifiers, ModifiersChangedEvent, Pixels, PlatformDisplay, PlatformInput, Point,
-    ScrollDelta, Size, TouchPhase, WindowParams, X11Window,
+    modifiers_from_xinput_info, point, px, AnyWindowHandle, Bounds, ClipboardItem, CursorStyle,
+    DisplayId, Keystroke, Modifiers, ModifiersChangedEvent, Pixels, PlatformDisplay, PlatformInput,
+    Point, ScrollDelta, Size, TouchPhase, WindowParams, X11Window,
 };
 
 use super::{
@@ -129,6 +129,7 @@ pub struct X11ClientState {
 
     pub(crate) common: LinuxCommon,
     pub(crate) clipboard: x11_clipboard::Clipboard,
+    pub(crate) clipboard_item: Option<ClipboardItem>,
 }
 
 #[derive(Clone)]
@@ -413,6 +414,7 @@ impl X11Client {
             scroll_y: None,
 
             clipboard,
+            clipboard_item: None,
         })))
     }
 
@@ -1097,7 +1099,7 @@ impl LinuxClient for X11Client {
     }
 
     fn write_to_clipboard(&self, item: crate::ClipboardItem) {
-        let state = self.0.borrow_mut();
+        let mut state = self.0.borrow_mut();
         state
             .clipboard
             .store(
@@ -1106,6 +1108,7 @@ impl LinuxClient for X11Client {
                 item.text().as_bytes(),
             )
             .ok();
+        state.clipboard_item.replace(item);
     }
 
     fn read_from_primary(&self) -> Option<crate::ClipboardItem> {
@@ -1127,6 +1130,20 @@ impl LinuxClient for X11Client {
 
     fn read_from_clipboard(&self) -> Option<crate::ClipboardItem> {
         let state = self.0.borrow_mut();
+        // if the last copy was from this app, return our cached item
+        // which has metadata attached.
+        if state
+            .clipboard
+            .setter
+            .connection
+            .get_selection_owner(state.clipboard.setter.atoms.clipboard)
+            .ok()
+            .and_then(|r| r.reply().ok())
+            .map(|reply| reply.owner == state.clipboard.setter.window)
+            .unwrap_or(false)
+        {
+            return state.clipboard_item.clone();
+        }
         state
             .clipboard
             .load(