Add some tests on adapted references with varargs and reflection

Also rename "varargAndDefaults" test directory to "adaptedReferences"

compiler/testData/codegen/box/callableReference/adaptedReferences/simpleEmptyVararg.kt

@@ -0,0 +1,11 @@
+// !LANGUAGE: +NewInference
+// IGNORE_BACKEND_FIR: JVM_IR
+
+fun foo(x: String, vararg y: String): String =
+        if (y.size == 0) x + "K" else "Fail"
+
+fun call(f: (String) -> String, x: String): String = f(x)
+
+fun box(): String {
+    return call(::foo, "O")
+}