assistant: Fixed "quote selection" with Vim visual line mode (#14713)

Previously, when using Vim mode and doing a line-wise visual selection,
the `assistant: quote selection` action would not work correctly, since
it would ignore that these were line-wise selections.

With this change, one can now select lines using visual line mode and
"quote selection works"

Release Notes:

- Fixes `assistant: quote selection` not working correctly when making
visual-line-mode selections in Vim mode.

crates/assistant/src/assistant_panel.rs

@@ -1685,9 +1685,11 @@ impl ContextEditor {
             return;
         };
 
+        let selection = editor.update(cx, |editor, cx| editor.selections.newest_adjusted(cx));
         let editor = editor.read(cx);
-        let range = editor.selections.newest::<usize>(cx).range();
         let buffer = editor.buffer().read(cx).snapshot(cx);
+        let range = editor::ToOffset::to_offset(&selection.start, &buffer)
+            ..editor::ToOffset::to_offset(&selection.end, &buffer);
         let start_language = buffer.language_at(range.start);
         let end_language = buffer.language_at(range.end);
         let language_name = if start_language == end_language {