[proposal] Heuristic interface to light parrallel solve call

[glelouet]

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The goal is to

• reduce the code required to make parallel search
• objectify the Strategy management, thus giving more visibility on the creation of strategies.

My proposal :

• a functional interface Heuristic, basically a Function<T extends Model, AbstractStrategy<?>> generating an AbstractStrategy from a Model.
• a new method in IResolutionHelper, namely <T extends Model> Solution findOptimalParallel(IntVar objective, boolean maximize, Function<T, T> modelDuplicator, Criterion stop, Heuristic... heuristics). This method creates a portfolio, iterate over the heuristics, uses the duplicator to duplicate the objective's model past first heuristic, configure this model with corresponding heuristics, then launches the search.

[glelouet]

https://github.com/chocoteam/choco-solver/pull/435

[glelouet]

no test yet though.