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/codegen/bytecodeListing/kt45853.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public class MyProblem {
+    // source: 'kt45853.kt'
+    public method <init>(): void
+    public @org.jetbrains.annotations.Nullable method getCause(): Exceptional
+}