Move formula compiler and runtime to separate module

[LeaVerou]

Mavo’s formula language is useful even outside of Mavo, and it may be nice to move to a separate library.
This will enable people to integrate it in other apps and frameworks, and will also improve maintainability through separation of concerns.
https://github.com/mavoweb/mavo/blob/main/src/functions.js
We still need to come up with a name (see #1011 )

Right now, these are the parts that would be moved there:

• All functions (except any Mavo-specific functions), i.e. https://github.com/mavoweb/mavo/blob/main/src/functions.js https://github.com/mavoweb/mavo/blob/main/src/functions.date.js https://github.com/mavoweb/mavo/blob/main/src/actions.js
• All code that converts to JS (i.e. the code in https://github.com/mavoweb/mavo/blob/main/src/mavoscript.js)
• The code in https://github.com/mavoweb/mavo/blob/main/src/data.js that resolves property references (though I'm hoping we can move a lot of that to be done statically).

Moving the compiler is likely far easier than moving the runtime, so we can start with that. I suspect a lot of this would be easier once we move to Vue (or another reactivity engine) and don't have to manage the reactivity ourselves (poorly).

This will be about compiling individual expressions, not interpolation with strings, so probably wouldn't include much code from

• https://github.com/mavoweb/mavo/blob/main/src/domexpression.js
• https://github.com/mavoweb/mavo/blob/main/src/expression.js