Specify type: do not suggest nullable type if not null is overridden

So #KT-12814 Fixed

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullFunction.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun notNullFun(): String
+}
+
+class Tesst : Base {
+    override fun notNullFun()<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullFunction.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun notNullFun(): String
+}
+
+class Tesst : Base {
+    override fun notNullFun(): String = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullProperty.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val notNull: String
+}
+
+class Tesst : Base {
+    override val notNull<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNotNullProperty.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val notNull: String
+}
+
+class Tesst : Base {
+    override val notNull: String = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableFunction.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun nullableFun(): String?
+}
+
+class Tesst : Base {
+    override fun nullableFun()<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableFunction.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    fun nullableFun(): String?
+}
+
+class Tesst : Base {
+    override fun nullableFun(): String? = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableProperty.kt

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val nullable: String?
+}
+
+class Tesst : Base {
+    override val nullable<caret> = java.lang.String.valueOf("")
+}

idea/testData/intentions/specifyTypeExplicitly/overrideNullableProperty.kt.after

@@ -0,0 +1,9 @@
+// CHOOSE_NULLABLE_TYPE_IF_EXISTS
+// WITH_RUNTIME
+interface Base {
+    val nullable: String?
+}
+
+class Tesst : Base {
+    override val nullable: String? = java.lang.String.valueOf("")
+}