Fix algorithm of determining modality for fake overrides

Previously we inferred "open" if there was at least one open member in the
hierarchy. However, that's not correct when that member is overridden by
another member in the hierarchy which is abstract. This led to incorrect code
being accepted by the front-end, and an exception during the bridge generation

 #KT-12467 Fixed

compiler/testData/diagnostics/tests/override/kt12467.kt

@@ -0,0 +1,14 @@
+interface A {
+    fun test() {
+    }
+}
+
+interface B : A {
+    override fun test()
+}
+
+interface C : A
+
+interface D : C, B
+
+<!ABSTRACT_MEMBER_NOT_IMPLEMENTED!>class K<!> : D