fix(iam): Modify addManagedPolicy to compare ARN instead of instance reference (#25529)

## Issue
When creating a role, the following warning message appeared:
```
Policy large: 11 exceeds 10 managed policies attached to a Role, this requires a quota increase
```

This was caused by the same managed policy being added multiple times.

Although there was only one managed policy in the created template, it appears that the managedPolicies field of the Role class has multiple instances of the same managed policy added to it.

----

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

Author: d0819

packages/aws-cdk-lib/aws-iam/lib/role.ts

@@ -549,7 +549,7 @@ export class Role extends Resource implements IRole {
     if (this._precreatedRole) {
       return this._precreatedRole.addManagedPolicy(policy);
     } else {
-      if (this.managedPolicies.find(mp => mp === policy)) { return; }
+      if (this.managedPolicies.some(mp => mp.managedPolicyArn === policy.managedPolicyArn)) { return; }
       this.managedPolicies.push(policy);
     }
   }

packages/aws-cdk-lib/aws-iam/test/role.test.ts

@@ -1166,7 +1166,18 @@ test('managed policy ARNs are deduplicated', () => {
       ManagedPolicy.fromAwsManagedPolicyName('SuperDeveloper'),
     ],
   });
-  role.addManagedPolicy(ManagedPolicy.fromAwsManagedPolicyName('SuperDeveloper'));
+  role.addToPrincipalPolicy(
+    new PolicyStatement({
+      actions: ['s3:*'],
+      resources: ['*'],
+    }),
+  );
+
+  for (let i = 0; i < 20; i++) {
+    role.addManagedPolicy(ManagedPolicy.fromAwsManagedPolicyName('SuperDeveloper'));
+  }
+
+  Annotations.fromStack(stack).hasNoWarning('/my-stack/MyRole', Match.stringLikeRegexp('.*'));
 
   Template.fromStack(stack).hasResourceProperties('AWS::IAM::Role', {
     ManagedPolicyArns: [
@@ -1184,6 +1195,26 @@ test('managed policy ARNs are deduplicated', () => {
   });
 });
 
+test('too many managed policies warning', () => {
+  const app = new App();
+  const stack = new Stack(app, 'my-stack');
+  const role = new Role(stack, 'MyRole', {
+    assumedBy: new ServicePrincipal('sns.amazonaws.com'),
+  });
+  role.addToPrincipalPolicy(
+    new PolicyStatement({
+      actions: ['s3:*'],
+      resources: ['*'],
+    }),
+  );
+
+  for (let i = 0; i < 20; i++) {
+    role.addManagedPolicy(ManagedPolicy.fromAwsManagedPolicyName(`SuperDeveloper${i}`));
+  }
+
+  Annotations.fromStack(stack).hasWarning('/my-stack/MyRole', Match.stringLikeRegexp('.*'));
+});
+
 describe('role with too large inline policy', () => {
   const N = 100;