R1:06778ea55032

Separate the "configuration" and "evaluation" phases of chart functions

Summary:
Depends on D20446. Currently, chart functions are both configured through arguments and evaluated through arguments. This sort of conflates things and makes some logic more difficult than it should be.

Instead:

- Function arguments are used to configure function behavior. For example, `scale(2)` configures a function which does `f(x) => 2 * x`.
- Evaluation is now separate, after configuration.

We can get rid of…