app-staging-synthesizer: Deletion of DefaultStagingStack fails when it does not contains any s3 asset

### Describe the bug

When using ` AppStagingSynthesizer.defaultResources` and we don't use any asset in stacks in the app, CFn `DependsOn` properties are not rendered properly on `DefaultStagingStack`.

This at least makes deleting the staging stack fail because a bucket policy sometimes gets deleted before `autoDeleteObject` custom resource ignoring its dependency.

### Expected Behavior

`DependsOn` properties are rendered.

### Current Behavior

`DependsOn` properties are not rendered.

### Reproduction Steps

Use the following code for cdk app.

```ts
// bin/cdk.ts
import 'source-map-support/register';
import * as cdk from 'aws-cdk-lib';
import { AppStagingSynthesizer, DeploymentIdentities } from '@aws-cdk/app-staging-synthesizer-alpha';

const app = new cdk.App({
defaultStackSynthesizer: AppStagingSynthesizer.defaultResources({
appId: 'my-app-id',
deploymentIdentities: DeploymentIdentities.defaultBootstrapRoles({ bootstrapRegion: 'us-east-1' }),
}),
});

// stack without any asset
new cdk.Stack(app, 'StagingSynthesizerStack');
```

Run `cdk synth` and check the output template (`StagingStack-my-app-id2-ACCOUNT-REGION.template.json`).

You can find this resource:

```json
"CdkStagingBucketAutoDeleteObjectsCustomResource800E998D": {
"Type": "Custom::S3AutoDeleteObjects",
"Properties": {
"ServiceToken": {
"Fn::GetAtt": [
"CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F",
"Arn"
]
},
"BucketName": {
"Ref": "CdkStagingBucket1636058C"
}
},
"UpdateReplacePolicy": "Delete",
"DeletionPolicy": "Delete"
},
```

Where it should be:

```diff
"CdkStagingBucketAutoDeleteObjectsCustomResource800E998D": {
"Type": "Custom::S3AutoDeleteObjects",
"Properties": {
"ServiceToken": {
"Fn::GetAtt": [
"CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F",
"Arn"
]
},
"BucketName": {
"Ref": "CdkStagingBucket1636058C"
}
},
+ "DependsOn": [
+ "CdkStagingBucketPolicy42BD1F92"
+ ],
"UpdateReplacePolicy": "Delete",
"DeletionPolicy": "Delete"
},
```

### Possible Solution
Here's my observation:

The root cause for this issue is that we add resources to an CDK app AFTER cdk runs `prepareApp` function.

https://github.com/aws/aws-cdk/blob/fce26b635d0ef2c443ca6d4e390a90f586130f05/packages/aws-cdk-lib/core/lib/private/synthesis.ts#L45

`Bucket` resource can be added even after `prepareApp` here (it's added on the first time `addFileAsset` is called) : https://github.com/aws/aws-cdk/blob/fce26b635d0ef2c443ca6d4e390a90f586130f05/packages/%40aws-cdk/app-staging-synthesizer-alpha/lib/app-staging-synthesizer.ts#L320

When we use any (s3) assets in the app (e.g. Lambda code asset), `addFileAsset` is called before `prepareApp`, so in that case it works as expected.

In `prepareApp` function, we search for all the dependencies between nodes and register them as a CFn resource dependencies. That's why dependencies added after `prepareApp` are not rendered at all.

https://github.com/aws/aws-cdk/blob/fce26b635d0ef2c443ca6d4e390a90f586130f05/packages/aws-cdk-lib/core/lib/private/prepare-app.ts#L17-L28

So the possible solution can be to always create a staging bucket first to avoid adding it after `prepareApp`. To do that, for example, we can add `this.getCreateBucket();` to the stack constructor here:

https://github.com/aws/aws-cdk/blob/fce26b635d0ef2c443ca6d4e390a90f586130f05/packages/%40aws-cdk/app-staging-synthesizer-alpha/lib/default-staging-stack.ts#L241-L246

I'm not quite sure if there is more thorough solution (given that there are possibly other resources other than a staging bucket that can be added after `prepareApp`). Afaik it seems only a staging bucket is causing this issue because the bucket is used to upload CFn templates in the app (that's why it can be added after `prepareApp`).

### Additional Information/Context

On the other hand, `DependsOn` of `CustomResourceProviderHandler` is rendered properly.

```json
"CustomS3AutoDeleteObjectsCustomResourceProviderHandler9D90184F": {
"Type": "AWS::Lambda::Function",
"Properties": {
},
"DependsOn": [
"CustomS3AutoDeleteObjectsCustomResourceProviderRole3B1BD092"
]
}
```

This is because custom resource provider uses `CfnResource.addDependency` directly instead of `Node.addDependency`.

https://github.com/aws/aws-cdk/blob/7c497ee998976b69ad1e2cd3e68f30cb593f8ded/packages/aws-cdk-lib/core/lib/custom-resource-provider/custom-resource-provider.ts#L313

### CDK CLI Version

2.104.0

### Framework Version

2.104.0

### Node.js Version

18

### OS

macOS

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_

Reproduce the issue with the provided TypeScript app and inspect the synthesized StagingStack template. Start with default-staging-stack.ts around the constructor and getCreateBucket(), then trace addFileAsset() in app-staging-synthesizer.ts alongside prepare-app.ts and synthesis.ts. Done means the staging bucket auto-delete resource retains its DependsOn relationship when no application asset is used, with deletion behavior covered by regression testing.

Written by the indexing model from the issue text.