JVM IR: Avoid direct invokes in callable reference tests

Due to the direct invoke optimization, most callable reference tests
were not generating callable references/lambdas.

compiler/testData/codegen/box/callableReference/bound/objectReceiver.kt

@@ -3,4 +3,4 @@ object Singleton {
     fun ok() = "OK"
 }
 
-fun box() = (Singleton::ok)()
+fun box() = (Singleton::ok).let { it() }