Introduce IrGetValue as a replacement for IrThisReference / IrGetExtensionReceiver / IrGetVariable.

compiler/testData/ir/irText/classes/outerClassAccess.kt

@@ -0,0 +1,20 @@
+class Outer {
+    fun foo() {}
+
+    inner class Inner {
+        fun test() {
+            foo()
+        }
+
+        inner class Inner2 {
+            fun test2() {
+                test()
+                foo()
+            }
+
+            fun Outer.test3() {
+                foo()
+            }
+        }
+    }
+}