[FIR] Check top-level property initialization via CFG

Now that files have a CFG, use it to validate properties are initialized
correctly. Update FirTopLevelPropertiesChecker to collect initialization
info for the property being checked - similar to
FirMemberPropertiesChecker - and validate proper initialization.

#KT-56683 Fixed
#KT-58531 Fixed

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -3242,6 +3242,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.kt");
             }
 
+            @Test
+            @TestMetadata("TopLevelPropertyInitialization.kt")
+            public void testTopLevelPropertyInitialization() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/TopLevelPropertyInitialization.kt");
+            }
+
             @Test
             @TestMetadata("ValDeferredInitInFinalClass.kt")
             public void testValDeferredInitInFinalClass() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -3242,6 +3242,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/backingField/SetterWithExplicitType.kt");
             }
 
+            @Test
+            @TestMetadata("TopLevelPropertyInitialization.kt")
+            public void testTopLevelPropertyInitialization() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/backingField/TopLevelPropertyInitialization.kt");
+            }
+
             @Test
             @TestMetadata("ValDeferredInitInFinalClass.kt")
             public void testValDeferredInitInFinalClass() throws Exception {