Automatic token expansion doesn't work if token is offscreen

[pokey]

Steps to reproduce

1. Put your cursor in the middle of a token
2. Scroll the token off the screen
3. Say "chuck first word"

Root cause

We use the navigation map to get tokens and the navigation map only has tokens that are on screen.

Proposed solution

Tokenise the line containing the start of the range and the line containing the end of the range and use those tokens