project_panel: Improve behavior for cut-pasting entries (#31931)

Previously, we would move entries each time they were pasted. Thus, if
you were to cut some files and pasted them in folder `a` and then `b`,
they would only occur in folder `b` and not in folder `a`. This is
unintuitive - e.g. the same does not apply to text and does not happen
in other editors.

This PR improves this behavior - after the first paste of a cut
clipboard, we change the clipboard to a copy clipboard, ensuring that
for all folloing pastes, the entries are not moved again. In the above
example, the files would then also be found in folder `a`. This is also
reflected in the added test.

Release Notes:

- Ensured that cut project panel entries are cut-pasted only on the
first use, and copy-pasted on all subsequent pastes.

crates/project_panel/src/project_panel.rs

@@ -2343,6 +2343,11 @@ impl ProjectPanel {
             })
             .detach_and_log_err(cx);
 
+            if clip_is_cut {
+                // Convert the clipboard cut entry to a copy entry after the first paste.
+                self.clipboard = self.clipboard.take().map(ClipboardEntry::to_copy_entry);
+            }
+
             self.expand_entry(worktree_id, entry.id, cx);
             Some(())
         });
@@ -5033,6 +5038,13 @@ impl ClipboardEntry {
             ClipboardEntry::Copied(entries) | ClipboardEntry::Cut(entries) => entries,
         }
     }
+
+    fn to_copy_entry(self) -> Self {
+        match self {
+            ClipboardEntry::Copied(_) => self,
+            ClipboardEntry::Cut(entries) => ClipboardEntry::Copied(entries),
+        }
+    }
 }
 
 #[cfg(test)]