Restore and deprecate Function{n}/ExtensionFunction{n} classes for easier migration

Users' Java code will not break in common cases (when passing functions to
Kotlin), and deprecation warnings will be reported.

Provide an inspection with a quick fix which allows to replace deprecated
function class usages to the new classes. Include this fix to the "code
cleanup" action

idea/testData/inspections/cleanup/DeprecatedFunctionClasses.java

@@ -0,0 +1,33 @@
+import kotlin.Function0;
+import kotlin.Function1;
+import kotlin.KotlinPackage;
+import kotlin.ExtensionFunction0;
+import kotlin.Unit;
+import kotlin.jvm.functions.Function2;
+
+public class DeprecatedFunctionClasses {
+    void f1(Function0 f) {
+        f.invoke();
+    }
+
+    void f2() {
+        KotlinPackage.map(new int[]{}, new Function1<Integer, Object>() {
+            @Override
+            public Object invoke(Integer integer) {
+                return null;
+            }
+        });
+    }
+
+    void f3(Function2<String, String, String> f) {
+    }
+
+    void f4(kotlin.Function0<Unit> g) {
+    }
+
+    void f5(kotlin.jvm.functions.Function1 f) {
+    }
+
+    void f6(ExtensionFunction0<String, Integer> e) {
+    }
+}