Give a proper definition of machine constants.

[HansOlsson]

They are compatible with text in the C-standard (so one can use DBL_EPS, DBL_MIN and DBL_MAX), and usable in practice. Closes #2056

[HansOlsson]

I guess the strings and values in ModelicaServices.Machine need to be adapted, too.

The strings obviously. The values - ideally yes, but that may break things in some bad models in MSL; thus it might be better to delay that if necessary.

[beutlich]

The values - ideally yes, but that may break things in some bad models in MSL; thus it might be better to delay that if necessary.

Yes, this might be the case and can be figured out during regression testing for a new MSL release. Otherwise, the description strings and the old values do not match. Thus, I am in favour to change both values and strings.