Summary:
- Make suggestions less case-sensitive (not entirely case-insensitive, but
allow top-level suggestions to match in all-lowercase)
- Add function signatures to suggestions for Grist functions.
- Excel-like functions that are present but not implemented are no longer
offered as suggestions.
Test Plan:
Added a test case on python side, and a browser test case for how suggestions
are rendered and inserted.
Reviewers: paulfitz
Reviewed By: paulfitz
Differential Revision: https://phab.getgrist.com/D2608
