Make a common class for UniqueCounter's, rename exprToJVM and jvmToExpr

src/main/scala/leon/codegen/CodeGeneration.scala

src/main/scala/leon/codegen/CompilationUnit.scala

src/main/scala/leon/codegen/CompiledExpression.scala

src/main/scala/leon/codegen/runtime/ChooseEntryPoint.scala

src/main/scala/leon/evaluators/DualEvaluator.scala

src/main/scala/leon/purescala/Common.scala

src/main/scala/leon/solvers/smtlib/SMTLIBSolver.scala

src/main/scala/leon/synthesis/rules/TEGISLike.scala

src/main/scala/leon/utils/UniqueCounter.scala