Fix (TypeScript): give datum an any type

[scottrippey]

What

The common props x, y, y0, and sortKey allow for "accessor" functions, like:

<VictoryLine
  data={data}
  x = {(datum) => datum.xValue}
  y = {(datum) => datum.yValue}
/>

Currently, we have the datum arg typed as object, which doesn't allow for any property access nor strong types (see #2360).

This PR allows for the type to be any. This seems like the best approach, since we currently don't know the shape of Datum, nor do we support generics with any of our components.
This will allow the above code to function properly, as well as support manually-added types (like (datum: MyData) => datum.xValue).

[gksander]

LGTM