[RFC]: add C implementation for `math/base/special/minmaxabs`

### Description

This RFC proposes adding C implementation for [`math/base/special/minmaxabs`](https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/math/base/special/minmaxabs).

```C
void stdlib_base_minmaxabs( const double x, const double y, double* minabs, double* maxabs )
```

### Related Issues

Related issues #649.

### Questions

No.

### Other

No.

### Checklist

- [X] I have read and understood the [Code of Conduct](https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md).
- [X] Searched for existing issues and pull requests.
- [X] The issue name begins with `RFC:`.

Start by reading the existing math/base/special/minmaxabs implementation and the related issue #649 to understand the proposed C API. Add the C implementation matching the stdlib_base_minmaxabs signature and verify that it is integrated with the package's existing implementation.

Scritto dal modello di indicizzazione a partire dal testo della issue.