zero_with_dimension

[blegat]

zero_with_dimension:
https://github.com/JuliaOpt/MathOptInterface.jl/blob/40aa3e542249200a1e3299b0e1d53978804c9e9a/src/Utilities/functions.jl#L300-L310
as added in #840.
But we should still

• Decide what's the best name
• Document it and add it in apireference.md
• Add standalone tests