ng g module with route option not working with the new provideRouter

### Command

generate

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

when using the new way `provideRouter` the command `ng g m foo --route=foo -m=app` stop working

### Minimal Reproduction

create new angular 15 project
in `app-routing.module.ts`

1. remove `AppRoutingModule`
2. export the `routes` const

in `app.module.ts`

1. remove `AppRoutingModule` from `import` array
2. add `provideRouter(routes)` to the `providers` array

then in the command line run `ng g m foo --route=foo -m=app`

### Exception or Error

```text
Couldn't find a route declaration in /src/app/app-routing.module.ts.
Use the '--module' option to specify a different routing module.
```

### Your Environment

```text
Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1500.5
@angular-devkit/build-angular 15.0.5
@angular-devkit/core 15.0.5
@angular-devkit/schematics 15.0.5
@angular/cli 15.0.5
@schematics/angular 15.0.5
rxjs 7.5.7
typescript 4.8.4
```

### Anything else relevant?

changing the file name from `app-routing.module.ts` to `routes.ts` gives a different but similar error message
```
Couldn't find a route declaration in /src/app/app.module.ts.
Use the '--module' option to specify a different routing module.
```

在使用 `provideRouter` 的 Angular 15 项目中复现 `ng g m foo --route=foo -m=app`，然后对照 `app-routing.module.ts` 和 `app.module.ts` 检查模块生成中的路由处理。完成标准是：该命令能够找到导出的路由声明，并在没有所示错误的情况下生成包含请求路由的模块。

由索引模型根据 Issue 内容生成。