Add find-replace-file tool, use it by default over edit-files-tool (#27438)

@agu-z and paired on trying out a "one tool call per edit" approach for
editing files. (The previous approach is still available, it's just
unchecked by default for now.)

Release Notes:

- N/A

---------

Co-authored-by: Agus <agus@zed.dev>

crates/assistant2/src/active_thread.rs

@@ -1256,7 +1256,7 @@ impl ActiveThread {
             "copy-path" => IconName::Clipboard,
             "delete-path" => IconName::Trash,
             "diagnostics" => IconName::Warning,
-            "edit-files" => IconName::Pencil,
+            "edit-files" | "find-replace-file" => IconName::Pencil,
             "fetch" => IconName::Globe,
             "list-directory" => IconName::Folder,
             "move-path" => IconName::ArrowRightLeft,