fix(cloudfront): auto-generated cache policy name might conflict cross-region (#13737)

This commit changes the auto-generated name of the `CachePolicy` to include stack name and region, thus providing unique name for the `CachePolicy` account-wide.

Closes #13629.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: robertd

packages/@aws-cdk/aws-cloudfront/lib/cache-policy.ts

@@ -1,4 +1,4 @@
-import { Duration, Names, Resource, Token } from '@aws-cdk/core';
+import { Duration, Names, Resource, Stack, Token } from '@aws-cdk/core';
 import { Construct } from 'constructs';
 import { CfnCachePolicy } from './cloudfront.generated';
 
@@ -125,7 +125,7 @@ export class CachePolicy extends Resource implements ICachePolicy {
       physicalName: props.cachePolicyName,
     });
 
-    const cachePolicyName = props.cachePolicyName ?? Names.uniqueId(this);
+    const cachePolicyName = props.cachePolicyName ?? `${Names.uniqueId(this)}-${Stack.of(this).region}`;
     if (!Token.isUnresolved(cachePolicyName) && !cachePolicyName.match(/^[\w-]+$/i)) {
       throw new Error(`'cachePolicyName' can only include '-', '_', and alphanumeric characters, got: '${props.cachePolicyName}'`);
     }

packages/@aws-cdk/aws-cloudfront/test/cache-policy.test.ts

@@ -24,7 +24,7 @@ describe('CachePolicy', () => {
 
     expect(stack).toHaveResource('AWS::CloudFront::CachePolicy', {
       CachePolicyConfig: {
-        Name: 'StackCachePolicy0D6FCBC0',
+        Name: 'StackCachePolicy0D6FCBC0-testregion',
         MinTTL: 0,
         DefaultTTL: 86400,
         MaxTTL: 31536000,