[PSI, FE, PSI2IR] Use labels for referencing specific receiver

compiler/testData/codegen/box/extensionFunctions/contextReceivers/this.kt

@@ -0,0 +1,20 @@
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_FIR: JVM_IR
+
+class A<T>(val a: T)
+class B(val b: Any?)
+
+context(A<String>, B) fun f() {
+    this@A.a.length
+    this@B.b
+}
+
+fun box(): String {
+    with(A("")) {
+        with(B(null)) {
+            f()
+        }
+    }
+    return "OK"
+}
+