Add continue_word_upwards_scrollback() and continue_word_downwards_offscreen()
to extend word selection beyond viewport boundaries, mirroring the line
selection fix. Add tests for word selection wrapping into scrollback and
below viewport.
Agent-Logs-Url: https://github.com/kovidgoyal/kitty/sessions/58191e45-d925-4996-b0d5-8b1bd4baa8d5
Co-authored-by: kovidgoyal <1308621+kovidgoyal@users.noreply.github.com>