Autocomplete argument highlighting gets confused by commas inside text()

Reported on ZenDesk.

To replicate:
1. Type text("Hello
2. see "message" highlighted in autocomplete tooltip above.
3. Type text("Hello, world
4. See "x" highlighted in autocomplete tooltip above.

This is a minor issue, not high priority.
I am guessing this would be addressed by @kevinb7's suggested refactoring of the autocomplete.

Reproduce the issue using the text() inputs described in the report, then trace the autocomplete argument-highlighting path and tooltip output. Done means commas inside text such as "Hello, world" no longer cause unrelated text to be highlighted in the autocomplete tooltip.

Written by the indexing model from the issue text.