JVM_IR KT-45853 include return type into Java method IdSignature

This is a hack required to accept [potentially] incorrect input
provided by the front-end; see KT-46042.

compiler/testData/ir/irText/classes/kt45853.kt

@@ -0,0 +1,25 @@
+// SKIP_KT_DUMP
+// DUMP_EXTERNAL_CLASS: X
+// DUMP_EXTERNAL_CLASS: AX
+// FILE: kt45853.kt
+
+abstract class A {
+    abstract val a: A?
+}
+
+class B() : AX() {
+    override fun getA(): X? = super.a
+}
+
+// FILE: X.java
+public interface X {
+    X getA();
+}
+
+// FILE: AX.java
+public abstract class AX extends A implements X {
+    @Override
+    public AX getA() {
+        return (AX) super.getA();
+    }
+}