Returning the cache in Mod.elabModValue breaks some models

[Per Östlund]

Mod.elabModValue previously didn't return the cache even though it used Ceval, which might be causing some issues with structural parameters (since information about them is stored in the cache). Returning the cache causes issues with some models though, so these issues needs to be fixed before we can return the cache. The only thing that needs to be done to return the cache from Mod.elabModValue is to replace the _ with outCache in the call to Ceval.ceval. The models that fail are:

IndexReduction.setVarKind failt because of wrong input:
simulation/libraries/3rdParty/Exercises/ServoSystem1.Aufgabe3_2.mos
simulation/libraries/3rdParty/Exercises/ServoSystem1.Aufgabe3_3.mos
simulation/libraries/3rdParty/Exercises/ServoSystem3.Aufgabe3_2.mos
simulation/libraries/3rdParty/Exercises/ServoSystem3.Aufgabe3_3.mos

Different result:
simulation/libraries/msl31/Modelica.Electrical.Machines.Examples.DCSE_Start.mos
simulation/libraries/msl32/Modelica.Electrical.Machines.Examples.Transformers.Rectifier12pulse.mos

Error: When solving linear system:
simulation/libraries/msl32/Modelica.Mechanics.MultiBody.Examples.Constraints.PrismaticConstraint.mos

Works fine, but shouldn't?:
simulation/modelica/others/ParameterCycle.mos

A lot of other test cases fail because of slightly different output, but none of them seem to be wrong from what I can see.

[Per Östlund]

Might still be an issue, but we no longer care about fixing issues in the old frontend.