[FIR] Report UNINITIALIZED_VARIABLE for top-level properties

When checking top-level properties, check with initialization enabled.
This makes sure the same errors are reported for member and top-level
properties.

compiler/testData/diagnostics/tests/controlFlowAnalysis/UninitializedOrReassignedVariables.fir.kt

@@ -255,7 +255,7 @@ class Outer() {
 }
 
 class ForwardAccessToBackingField() { //kt-147
-    val a = <!TYPECHECKER_HAS_RUN_INTO_RECURSIVE_PROBLEM, UNINITIALIZED_VARIABLE!>a<!> // error
+    val a = <!TYPECHECKER_HAS_RUN_INTO_RECURSIVE_PROBLEM!>a<!> // error
     val b = <!UNINITIALIZED_VARIABLE!>c<!> // error
     val c = 1
 }