Add MapEqualValueKeys primitive

...scala/inox/solvers/unrolling/MapEqualValueKeysSuite.scala

src/main/scala/inox/ast/Deconstructors.scala

src/main/scala/inox/ast/Expressions.scala

src/main/scala/inox/ast/Printers.scala

src/main/scala/inox/evaluators/RecursiveEvaluator.scala

src/main/scala/inox/solvers/smtlib/Z3Target.scala

src/main/scala/inox/solvers/z3/Z3Native.scala

src/main/scala/inox/utils/Serialization.scala