[enhancement] apfloat functions should take additional configuration

### What's hard to do? (limit 100 words)

In a few discussions, it has come up that the behavior of apfloat functions should really enable more control over their behavior regarding rounding, conversion of special values (e.g. NaN), and so forth.

Currently, many functions neither expose some control nor clearly state their fixed behavior in the naming.

### Current best alternative workaround (limit 100 words)

In some cases, we explicitly include some of the behavior in the name, while in other cases, it's only described in the documentation.

### Your view of the "best case XLS enhancement" (limit 100 words)

Some sort of function parameterization that allows these to be configured.