FIR checker: report VIRTUAL_MEMBER_HIDDEN

compiler/fir/analysis-tests/testData/resolve/overrides/simple.kt

@@ -8,7 +8,7 @@ open class A {
 
 class B : A() {
     override fun foo(): B = this
-    fun bar(): B = this // Ambiguity, no override here (really it's just "missing override" and no ambiguity)
+    fun <!VIRTUAL_MEMBER_HIDDEN!>bar<!>(): B = this // Missing 'override'
     override fun buz(p: B): B = this //No override as B not :> A
 
     fun test() {