[FIR] add support for varargs in delegated constructor calls

Also add support for spread operators as named arguments.

compiler/testData/codegen/box/innerNested/superConstructorCall/objectExtendsClassVararg.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 open class SomeClass(val some: Double, val other: Int, vararg val args: String) {
     fun result() = args[1]
 }