Support disabling drag-and-drop in Project Panel (#36719)

Release Notes:

- Added setting for disabling drag and drop in project panel. `{
"project_panel": {"drag_and_drop": false } }`

docs/src/configuring-zed.md

@@ -3243,6 +3243,7 @@ Run the `theme selector: toggle` action in the command palette to see a current
     "indent_size": 20,
     "auto_reveal_entries": true,
     "auto_fold_dirs": true,
+    "drag_and_drop": true,
     "scrollbar": {
       "show": null
     },

docs/src/visual-customization.md

@@ -431,6 +431,7 @@ Project panel can be shown/hidden with {#action project_panel::ToggleFocus} ({#k
     "auto_reveal_entries": true,    // Show file in panel when activating its buffer
     "auto_fold_dirs": true,         // Fold dirs with single subdir
     "sticky_scroll": true,          // Stick parent directories at top of the project panel.
+    "drag_and_drop": true,          // Whether drag and drop is enabled
     "scrollbar": {                  // Project panel scrollbar settings
       "show": null                  // Show/hide: (auto, system, always, never)
     },