[FIR] Add tests for top-level property initialization in scripts

- The test data is missing initialization checks and will be fixed with
  the subsequent commit.
- The test data is originally taken from
  `backingField/TopLevelPropertyInitialization` and has been simplified.
- I didn't add `const val` properties to the test data (compared to the
  original) due to KT-20110.

^KT-63286

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

@@ -30288,6 +30288,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/script/topLevelPropertiesWithGetSet.kts");
             }
 
+            @Test
+            @TestMetadata("topLevelPropertyInitialization.kts")
+            public void testTopLevelPropertyInitialization() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/script/topLevelPropertyInitialization.kts");
+            }
+
             @Test
             @TestMetadata("topLevelVariable.kts")
             public void testTopLevelVariable() throws Exception {

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

@@ -30288,6 +30288,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/script/topLevelPropertiesWithGetSet.kts");
             }
 
+            @Test
+            @TestMetadata("topLevelPropertyInitialization.kts")
+            public void testTopLevelPropertyInitialization() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/script/topLevelPropertyInitialization.kts");
+            }
+
             @Test
             @TestMetadata("topLevelVariable.kts")
             public void testTopLevelVariable() throws Exception {