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/traits/traitWithPrivateMemberAccessFromLambda.kt

@@ -1,11 +1,11 @@
 interface Z {
 
     fun testFun(): String {
-        return { privateFun() } ()
+        return { privateFun() }.let { it() }
     }
 
     fun testProperty(): String {
-        return { privateProp } ()
+        return { privateProp }.let { it() }
     }
 
     private fun privateFun(): String {