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/jvmField/captureClassFields.kt

@@ -10,7 +10,7 @@ open class A {
     fun test(): String {
         return {
             publicField + internalField + protectedField
-        }()
+        }.let { it() }
     }
 }