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.