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/tests/PackageQualified.fir.kt

@@ -25,7 +25,7 @@ package foobar.a
 
 // FILE: d.kt
 package foobar
-val x1 = <!UNRESOLVED_REFERENCE!>a<!>.<!UNRESOLVED_REFERENCE!>a<!>
+val x1 = <!UNRESOLVED_REFERENCE!>a<!>.a
 val x2 = foobar.a.a
 
 val y1 = foobar.a.b