[FIR] Move check for _private-to-this_ visibility into checker

^KT-55446
^KT-65790 Fixed

compiler/testData/diagnostics/tests/visibility/privateToThis.fir.kt

@@ -1,5 +1,6 @@
 // FIR_DUMP
 
+// explicit types
 class A<in T>(t: T) {
     private val t: T = t  // PRIVATE_TO_THIS
 
@@ -24,3 +25,13 @@ class A<in T>(t: T) {
         }
     }
 }
+
+// implicit types
+class C<in T>(t: T) {
+    private val t: T = t
+    private val tt = t
+
+    fun foo(a: C<String>) {
+        val x: String = a.<!INVISIBLE_REFERENCE!>tt<!>
+    }
+}