Override/Implement Members: Do not make return type non-nullable if base

return type is explicitly nullable
 #KT-13383 Fixed
 #KT-13379 Fixed

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

@@ -0,0 +1,9 @@
+package foo;
+
+import org.jetbrains.annotations.Nullable;
+
+public class A {
+    public @Nullable String foo(String s) {
+        return null;
+    }
+}

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

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

idea/testData/codeInsight/overrideImplement/nullableJavaType/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>
+    }
+}

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

@@ -0,0 +1,7 @@
+interface IBase {
+    fun foo(): Any?
+}
+
+class C : IBase {
+    <caret>
+}

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

@@ -0,0 +1,9 @@
+interface IBase {
+    fun foo(): Any?
+}
+
+class C : IBase {
+    override fun foo(): Any? {
+        <selection><caret>TODO("not implemented") //To change body of created functions use File | Settings | File Templates.</selection>
+    }
+}