Reporting ACCIDENTAL_OVERRIDE on jvm signatures that have no descriptors

(marking them SYNTHETIC)

compiler/testData/diagnostics/tests/duplicateJvmSignature/accidentalOverrides/defaultFunction.kt

@@ -0,0 +1,9 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+open class Base {
+    open fun `foo$default`(d: Derived, i: Int, mask: Int) {}
+}
+
+class Derived : Base() {
+    <!ACCIDENTAL_OVERRIDE!>fun foo(i: Int = 0)<!> {}
+}