Stop using JFunction{0, 1, 2}

Since Scala 2.12, the regular scala.Function{0, 1, 2} are valid SAM
types, so these interfaces aren't needed anymore.

Author: smarter

compiler/src/dotty/tools/backend/jvm/BCodeBodyBuilder.scala

@@ -328,7 +328,6 @@ trait BCodeBodyBuilder extends BCodeSkelBuilder {
               val arity = app.meth.tpe.widenDealias.firstParamTypes.size - env.size
               val returnsUnit = app.meth.tpe.widenDealias.resultType.classSymbol == defn.UnitClass
               if (returnsUnit) requiredClass(("scala.runtime.function.JProcedure" + arity))
-              else if (arity <= 2) requiredClass(("scala.runtime.function.JFunction" + arity))
               else requiredClass(("scala.Function" + arity))
             }
           }

library/src/scala/runtime/function/JFunction0.java renamed to library/src-non-bootstrapped/scala/runtime/function/JFunction0.java

@@ -8,7 +8,7 @@
 import scala.runtime.BoxedUnit;
 
 @FunctionalInterface
-public interface JProcedure0 extends JFunction0<BoxedUnit>, java.io.Serializable {
+public interface JProcedure0 extends scala.Function0<BoxedUnit>, java.io.Serializable {
     void applyVoid();
 
     default BoxedUnit apply() {

library/src/scala/runtime/function/JFunction1.java renamed to library/src-non-bootstrapped/scala/runtime/function/JFunction1.java

@@ -8,7 +8,7 @@
 import scala.runtime.BoxedUnit;
 
 @FunctionalInterface
-public interface JProcedure1<T1> extends JFunction1<T1, BoxedUnit>, java.io.Serializable {
+public interface JProcedure1<T1> extends scala.Function1<T1, BoxedUnit>, java.io.Serializable {
     void applyVoid(T1 t1);
 
     default BoxedUnit apply(T1 t1) {

library/src/scala/runtime/function/JFunction2.java renamed to library/src-non-bootstrapped/scala/runtime/function/JFunction2.java

@@ -8,7 +8,7 @@
 import scala.runtime.BoxedUnit;
 
 @FunctionalInterface
-public interface JProcedure2<T1, T2> extends JFunction2<T1, T2, BoxedUnit>, java.io.Serializable {
+public interface JProcedure2<T1, T2> extends scala.Function2<T1, T2, BoxedUnit>, java.io.Serializable {
     void applyVoid(T1 t1, T2 t2);
 
     default BoxedUnit apply(T1 t1, T2 t2) {