Allow disabling editor scrollbars programmatically (#22333)

Disable them in the diff editors

Closes https://github.com/zed-industries/zed/issues/22271

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -1556,6 +1556,7 @@ impl ContextEditor {
             let mut editor = Editor::for_buffer(context.read(cx).buffer().clone(), None, cx);
             editor.set_soft_wrap_mode(SoftWrap::EditorWidth, cx);
             editor.set_show_line_numbers(false, cx);
+            editor.set_show_scrollbars(false, cx);
             editor.set_show_git_diff_gutter(false, cx);
             editor.set_show_code_actions(false, cx);
             editor.set_show_runnables(false, cx);