git: Add git stash picker (#35927)

Closes #ISSUE

This PR continues work from #32821 by adding a stash entry picker for
pop/drop operations. Additionally, the stash pop action in the git panel
is now disabled when no stash entries exist, preventing error logs from
attempted pops on empty stashes.

Preview:

<img width="1920" height="1256" alt="Screenshot From 2025-09-11
14-08-31"
src="https://github.com/user-attachments/assets/b2f32974-8c69-4e50-8951-24ab2cf93c12"
/>

<img width="1920" height="1256" alt="Screenshot From 2025-09-11
14-08-12"
src="https://github.com/user-attachments/assets/992ce237-43c9-456e-979c-c2e2149d633e"
/>



Release Notes:

- Added a stash picker to pop and drop a specific stash entry
- Disabled the stash pop action on the git panel when no stash entries
exist
- Added git stash apply command
- Added git stash drop command

assets/keymaps/default-linux.json

@@ -1075,6 +1075,12 @@
       "ctrl-backspace": "tab_switcher::CloseSelectedItem"
     }
   },
+  {
+    "context": "StashList || (StashList > Picker > Editor)",
+    "bindings": {
+      "ctrl-shift-backspace": "stash_picker::DropStashItem"
+    }
+  },
   {
     "context": "Terminal",
     "bindings": {