Feature request: variable bounds

[maxkratz]

It would be nice if (extra) mapping variables and type variables could be configured to have bounds.
We have to come up with a way to change GIPSL such that the following combinations are possible:

• only lower bound
• only upper bound
• lower and upper bounds are specified

Currently, it is necessary to specify bounds via explicit constraints, e.g.: https://github.com/maxkratz/dissertation-ihtp/blob/feature/ihtc-virtual-many-references-diss/ihtcvirtualgipssolution/src/ihtcvirtualgipssolution/Model.gipsl#L609-L612