Benchmark: refactors Dep_graph with a better graph types, with fixing the inference result override

Refactoring of Dep_graph. It is the first step towards the correct dependencies between benchmarks.

Now the dependency graph has Solver.solved as verticies, instead of the string name of benchmarks.

It also fixes the bug #4922 (closed) partially by allowing inferred value overload only for those provided by a solution.

Note that this MR itself does not change the dependency analysis at all.