FIR checker: skip error named reference if receiver is unresolved

Currently, FIR reports errors caused by previous resolution failure. For
example with unresolved `a` and `b` in code `a.b`, both `a` and `b` are
highlighted. FE1.0 only highlights `a` since it's the root cause. This
change applies this heuristics when reporting FirDiagnostics.

compiler/testData/diagnostics/testsWithStdLib/coroutines/kt18292.fir.kt

@@ -14,6 +14,6 @@ suspend fun fib(n: Long) =
     async {
         when {
             n < 2 -> n
-            else -> fib(n - 1).<!UNRESOLVED_REFERENCE!>await<!>() <!AMBIGUITY!>+<!> fib(n - 2).<!UNRESOLVED_REFERENCE!>await<!>()
+            else -> fib(n - 1).<!UNRESOLVED_REFERENCE!>await<!>() + fib(n - 2).<!UNRESOLVED_REFERENCE!>await<!>()
         }
     }