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

compiler/testData/diagnostics/tests/extensions/contextReceivers/thisWithReceiverLabelsFunctions.kt

@@ -0,0 +1,17 @@
+class A<T>(val a: T)
+class B(val b: Any)
+class C(val c: Any)
+
+context(A<Int>, A<String>, B) fun f() {
+    this@A.a.length
+    this@B.b
+    <!NO_THIS!>this<!>
+}
+
+context(A<Int>, A<String>, B) fun C.f() {
+    this@A.a.length
+    this@B.b
+    this@C.c
+    this@f.c
+    this.c
+}