Move until function to toolbox

[adriamurphy]

In the Snap templates, there is a script called functions.js with a handy function called until.
https://github.com/searchspring/snapfu-template-preact/blob/production/src/scripts/functions.js

For a long time, there has been a "to-do" comment in this file to move to the Snap toolbox:

// TODO - move to toolbox

I did not see an issue for this, so I wanted to log one to ensure it gets moved there at some point.