FIR: Support checking PRIVATE_TO_THIS visibility #KT-49875 Fixed

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

@@ -9,6 +9,6 @@ class A<in T>(t: T) {
     }
 
     fun foo(a: A<String>) {
-        val x: String = a.t // Invisible!
+        val x: String = a.<!INVISIBLE_REFERENCE!>t<!> // Invisible!
     }
 }

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

@@ -13,7 +13,7 @@ FILE: privateToThis.fir.kt
         }
 
         public final fun foo(a: R|A<kotlin/String>|): R|kotlin/Unit| {
-            lval x: R|kotlin/String| = R|<local>/a|.R|SubstitutionOverride</A.t: R|kotlin/String|>|
+            lval x: R|kotlin/String| = R|<local>/a|.<HIDDEN: /A.t is invisible>#
         }
 
     }