fix(migrations): resolve error in standalone migration (#56302)

This is related to an issue that was reported internally. We were assuming that `hasNgModuleMetadataElements` will return true only for property assignments initialized to arrays, but that's not the case.

These changes update the type and our assertions to more accurately reflect the AST and to avoid the error.

PR Close #56302

packages/core/schematics/ng-generate/standalone-migration/to-standalone.ts

@@ -517,9 +517,7 @@ function findImportLocation(
  * E.g. `declarations: [Foo]` or `declarations: SOME_VAR` would match this description,
  * but not `declarations: []`.
  */
-function hasNgModuleMetadataElements(
-  node: ts.Node,
-): node is ts.PropertyAssignment & {initializer: ts.ArrayLiteralExpression} {
+function hasNgModuleMetadataElements(node: ts.Node): node is ts.PropertyAssignment {
   return (
     ts.isPropertyAssignment(node) &&
     (!ts.isArrayLiteralExpression(node.initializer) || node.initializer.elements.length > 0)
@@ -788,7 +786,9 @@ function analyzeTestingModules(
 
     const importsProp = findLiteralProperty(obj, 'imports');
     const importElements =
-      importsProp && hasNgModuleMetadataElements(importsProp)
+      importsProp &&
+      hasNgModuleMetadataElements(importsProp) &&
+      ts.isArrayLiteralExpression(importsProp.initializer)
         ? importsProp.initializer.elements.filter((el) => {
             // Filter out calls since they may be a `ModuleWithProviders`.
             return (
@@ -847,7 +847,11 @@ function extractDeclarationsFromTestObject(
   const results: ts.ClassDeclaration[] = [];
   const declarations = findLiteralProperty(obj, 'declarations');
 
-  if (declarations && hasNgModuleMetadataElements(declarations)) {
+  if (
+    declarations &&
+    hasNgModuleMetadataElements(declarations) &&
+    ts.isArrayLiteralExpression(declarations.initializer)
+  ) {
     for (const element of declarations.initializer.elements) {
       const declaration = findClassDeclaration(element, typeChecker);