Specify type explicitly: suggest also types from overridden

So #KT-22092 Fixed

idea/testData/intentions/specifyTypeExplicitly/overriddenAsNull.kt

@@ -0,0 +1,9 @@
+// DO_NOT_CHOOSE_NOTHING
+
+interface I {
+    fun foo(): String?
+}
+
+class Test : I {
+    override fun foo()<caret> = null
+}

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

@@ -0,0 +1,9 @@
+// DO_NOT_CHOOSE_NOTHING
+
+interface I {
+    fun foo(): String?
+}
+
+class Test : I {
+    override fun foo(): String? = null
+}