Introduce FunctionFlags. Remove all other mutability from FunDef (except body).

src/main/scala/leon/Main.scala

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/purescala/Definitions.scala

src/main/scala/leon/purescala/ExprOps.scala

src/main/scala/leon/purescala/FunctionClosure.scala

src/main/scala/leon/purescala/MethodLifting.scala

src/main/scala/leon/purescala/PrettyPrinter.scala

src/main/scala/leon/purescala/RestoreMethods.scala

src/main/scala/leon/purescala/ScopeSimplifier.scala

...main/scala/leon/solvers/templates/TemplateGenerator.scala

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

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

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

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

...main/scala/leon/synthesis/rules/IntegerInequalities.scala

src/main/scala/leon/termination/StructuralSize.scala

src/main/scala/leon/utils/PreprocessingPhase.scala

src/main/scala/leon/utils/ScopingPhase.scala

src/main/scala/leon/utils/UnitElimination.scala

src/main/scala/leon/xlang/EpsilonElimination.scala