Report diagnostic on overrides of experimental members

Unless they're experimental themselves

 #KT-22759 In Progress

compiler/testData/diagnostics/testsWithStdLib/experimental/errors.kt

@@ -0,0 +1,28 @@
+// !API_VERSION: 1.3
+// MODULE: api
+// FILE: api.kt
+
+package api
+
+@Experimental(Experimental.Level.ERROR, [Experimental.Impact.COMPILATION])
+annotation class E
+
+open class Base {
+    @E
+    open fun foo() {}
+}
+
+// MODULE: usage(api)
+// FILE: usage.kt
+
+package usage
+
+import api.*
+
+class Derived : Base() {
+    override fun <!EXPERIMENTAL_OVERRIDE_ERROR!>foo<!>() {}
+}
+
+fun test(b: Base) {
+    b.<!EXPERIMENTAL_API_USAGE_ERROR!>foo<!>()
+}