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/defaultArguments/protected.kt

@@ -14,7 +14,7 @@ import foo.Foo
 
 class Bar() : Foo() {
     fun execute(): String {
-        return { foo() } ()
+        return { foo() }.let { it() }
     }
 }