restrict anonym -> lambda: reject if return type would be changed (IDEA-154805)

java/typeMigration/testData/inspections/guava/transformAndConcat3_after.java

@@ -1,4 +1,5 @@
 import java.util.ArrayList;
+import java.util.function.Function;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
@@ -7,16 +8,19 @@ class A {
     ArrayList<String> strings = new ArrayList<String>();
     Stream<String> it = strings.stream();
 
-    int i = (int) it.flatMap(o -> {
-        if ('a' > 2) {
-            return StreamSupport.stream(getIterable().spliterator(), false);
-        } else if ('c' < 123) {
-            ArrayList<String> strings1 = new ArrayList<>();
-            strings1.add(o);
-            return strings1.stream();
+    int i = (int) it.flatMap((o) -> StreamSupport.stream(new Function<String, Iterable<String>>() {
+        @Override
+        public Iterable<String> apply(String o) {
+            if ('a' > 2) {
+                return getIterable();
+            } else if ('c' < 123) {
+                ArrayList<String> strings1 = new ArrayList<>();
+                strings1.add(o);
+                return strings1;
+            }
+            return null;
         }
-        return null;
-    }).count();
+    }.apply(o).spliterator(), false)).count();
 
   }