[FIR] Improve diagnostic reporting & don't use error symbol for candidate if possible

Also introduce few new diagnostics:
- NONE_APPLICABLE more many inapplicable candidates
- HIDDEN for visible candidates

compiler/testData/diagnostics/tests/override/AllPrivateFromSuperTypes.fir.kt

@@ -10,5 +10,5 @@ open class C {
 }
 
 class Subject : C(), A {
-    val c = <!INAPPLICABLE_CANDIDATE!>a<!>
-}
+    val c = <!HIDDEN!>a<!>
+}