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?
I think that makes the most sense; just replace
```
vec4 pos = $transform(vec4(0.0, 0.0, 0.0, 1.0));
```
with
```
vec4 pos = $transform(u_pos);
```