agent: Allow to accept and reject all via the panel (#31971)

This PR introduces the "Reject All" and "Accept All" buttons in the
panel's edit bar, which appears as soon as the agent starts editing a
file. I'm also adding here a new method to the thread called
`has_pending_edit_tool_uses`, which is a more specific way of knowing,
in comparison to the `is_generating` method, whether or not the
reject/accept all actions can be triggered.

Previously, without this new method, you'd be waiting for the whole
generation to end (e.g., the agent would be generating markdown with
things like change summary) to be able to click those buttons, when the
edit was already there, ready for you. It always felt like waiting for
the whole thing was unnecessary when you really wanted to just wait for
the _edits_ to be done, as so to avoid any potential conflicting state.

<img
src="https://github.com/user-attachments/assets/0927f3a6-c9ee-46ae-8f7b-97157d39a7b5"
width="500"/>

---

Release Notes:

- agent: Added ability to reject and accept all changes from the agent
panel.

---------

Co-authored-by: Agus Zubiaga <hi@aguz.me>

assets/icons/list_todo.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="lucide lucide-list-todo-icon lucide-list-todo"><rect x="3" y="5" width="6" height="6" rx="1"/><path d="m3 17 2 2 4-4"/><path d="M13 6h8"/><path d="M13 12h8"/><path d="M13 18h8"/></svg>