Store and derive information from function call images

It would be great to support images on specific function calls, and derive additional information from it.

- Under the assumption that `x` is an integer and given the information that `x^3` is nonnegative, we should be able to derive that `x` is nonnegative. Additionally, we should be able to determine that `x^5` should be nonnegative.
- Given the knowledge that the function call `f(2)` is greater than 7, we should infer that `abs(f(2))` can be rewritten to `f(2)`, even though we know nothing about `f` itself.

The issue names no files, tests, or entry points, so first map the function-call representation and existing simplification rules. Define how stored image information is associated with calls and how derived sign facts affect rewriting. Done means the stated integer-power and absolute-value examples are supported by tests.

Written by the indexing model from the issue text.