FIR: implement diagnostics for qualifier as stand-alone expression case

compiler/testData/diagnostics/tests/resolve/constructorVsCompanion.fir.kt

@@ -16,8 +16,8 @@ class E private constructor() {
     }
 }
 
-val a = A
+val a = <!NO_COMPANION_OBJECT!>A<!>
 val <!EXPOSED_PROPERTY_TYPE!>b<!> = B
-val c = C
+val c = <!NO_COMPANION_OBJECT!>C<!>
 val d = D
 val e = E(42)