Override/Implement: Prefer not-nullable return type when overriding Java method without nullability annotation

#KT-12381 Fixed
(cherry picked from commit 2b87f8e)

idea/testData/codeInsight/overrideImplement/implementJavaRawSubclass/foo/Impl.kt.after

@@ -2,7 +2,7 @@ import foo.A
 import foo.B
 
 class C : A() {
-    override fun foo(x: MutableList<Any?>?, y: String?): B<*>? {
+    override fun foo(x: MutableList<Any?>?, y: String?): B<*> {
         <selection><caret>throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.</selection>
     }
 }

idea/testData/codeInsight/overrideImplement/javaInterfaceMethod/foo/Impl.kt.after

@@ -1,7 +1,7 @@
 import foo.Intf
 
 class Impl(): Intf {
-    override fun getFooBar(): String? {
+    override fun getFooBar(): String {
         <selection><caret>throw UnsupportedOperationException("not implemented") //To change body of created functions use File | Settings | File Templates.</selection>
     }
 }

idea/testData/codeInsight/overrideImplement/javaMethodWithPackageProtectedVisibility/foo/Impl.kt.after

@@ -3,7 +3,7 @@ package foo
 import foo.Intf
 
 class Impl(): Intf() {
-    override fun getFooBar(): String? {
+    override fun getFooBar(): String {
         <selection><caret>return super.getFooBar()</selection>
     }
 }

idea/testData/codeInsight/overrideImplement/javaMethodWithPackageVisibility/foo/Impl.kt.after

@@ -3,7 +3,7 @@ package foo
 import foo.Intf
 
 class Impl(): Intf() {
-    override fun getFooBar(): String? {
+    override fun getFooBar(): String {
         <selection><caret>return super.getFooBar()</selection>
     }
 }

idea/testData/codeInsight/overrideImplement/platformTypes/foo/A.java

@@ -0,0 +1,7 @@
+package foo;
+
+public class A {
+    public String foo(String s) {
+        return null;
+    }
+}

idea/testData/codeInsight/overrideImplement/platformTypes/foo/Impl.kt

@@ -0,0 +1,5 @@
+import foo.A
+
+class B : A() {
+    <caret>
+}

idea/testData/codeInsight/overrideImplement/platformTypes/foo/Impl.kt.after

@@ -0,0 +1,7 @@
+import foo.A
+
+class B : A() {
+    override fun foo(s: String?): String {
+        <selection><caret>return super.foo(s)</selection>
+    }
+}