Text has point_size and pos properties

And text always draws in that point size, even if inside a viewbox. There are two things to fix, see todo items:

* Is the pointsize correct like this?
* How to prevent recompilation on each draw?
But if I add a print statement in `ModularProgram._build()` I see it gets printed on each draw ... If I print `xform` I can see that it is indeed the same object (a FunctionChain):