Basic class members generation.

Split testData into 'classes' and 'expressions'.

compiler/testData/ir/irText/expressions/references.kt

@@ -0,0 +1,17 @@
+val ok = "OK"
+val ok2 = ok
+val ok3: String get() = "OK"
+
+fun test1() = ok
+
+fun test2(x: String) = x
+
+fun test3(): String {
+    val x = "OK"
+    return x
+}
+
+fun test4() = ok3
+
+val String.okext: String get() = "OK"
+fun String.test5() = okext