Implicit receiver smart casts implementation and highlighting

compiler/testData/diagnostics/tests/smartCasts/implicitReceiver.kt

@@ -0,0 +1,24 @@
+open class A {
+    class B : A() {
+        val a = "FAIL"
+    }
+
+    fun foo(): String {
+        if (this is B) return <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>a<!>
+        return "OK"
+    }
+}
+
+fun A?.bar() {
+    if (this != null) <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>foo<!>()
+}
+
+fun A.gav() = if (this is A.B) <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>a<!> else ""
+
+class C {
+    fun A?.complex(): String {
+        if (this is A.B) return <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>a<!>
+        else if (this != null) return <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>foo<!>()
+        else return ""
+    }
+}