Support MA.Zero in objective and constraints

[odow]

Closes #2087

[odow]

@blegat did that latest tag of MA break these tests?

[odow]

Failing tests will be fixed with jump-dev/MutableArithmetics.jl#46.

[codecov]

Codecov Report

Merging #2219 into master will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2219      +/-   ##
==========================================
- Coverage   91.11%   91.06%   -0.05%     
==========================================
  Files          42       42              
  Lines        4130     4208      +78     
==========================================
+ Hits         3763     3832      +69     
- Misses        367      376       +9     

Impacted Files	Coverage Δ
src/macros.jl	92.65% <100.00%> (+0.01%)	⬆️
src/objective.jl	91.66% <100.00%> (+0.23%)	⬆️
src/JuMP.jl	77.68% <0.00%> (+3.12%)	⬆️
src/sets.jl	94.73% <0.00%> (+9.02%)	⬆️

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