fix(CLI): sam resources hidden in changeset diffs (#29223)

### Issue # (if applicable)

Closes #29185

### Reason for this change

CFN applies the SAM transform before the changeset is created. This means that SAM resources become their underlying CFN types in the template that the changeset operates on. This means that the changeset is operating on resources that we don't see in our template. 

### Description of changes

Before, if we saw properties in our diff that were not in the changeset (like `codeUri` for `Serverless::Function`, which doesn't appear in the changeset, because it becomes `Code` for `Lambda::Function`), we'd filter them out of the diff. We now skip this process for SAM resources.

### Description of how you validated changes

unit test

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: comcalvi

packages/@aws-cdk/cloudformation-diff/lib/diff-template.ts

@@ -221,6 +221,10 @@ function addImportInformation(diff: types.TemplateDiff, changeSet: CloudFormatio
 function filterFalsePositivies(diff: types.TemplateDiff, changeSet: CloudFormation.DescribeChangeSetOutput) {
   const replacements = findResourceReplacements(changeSet);
   diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
+    if (change.resourceType.includes('AWS::Serverless')) {
+      // CFN applies the SAM transform before creating the changeset, so the changeset contains no information about SAM resources
+      return;
+    }
     change.forEachDifference((type: 'Property' | 'Other', name: string, value: types.Difference<any> | types.PropertyDifference<any>) => {
       if (type === 'Property') {
         if (!replacements[logicalId]) {

packages/@aws-cdk/cloudformation-diff/test/diff-template.test.ts

@@ -1118,6 +1118,55 @@ describe('changeset', () => {
     expect(differences.resources.differenceCount).toBe(1);
   });
 
+  test('SAM Resources are rendered with changeset diffs', () => {
+    // GIVEN
+    const currentTemplate = {
+      Resources: {
+        ServerlessFunction: {
+          Type: 'AWS::Serverless::Function',
+          Properties: {
+            CodeUri: 's3://bermuda-triangle-1337-bucket/old-handler.zip',
+          },
+        },
+      },
+    };
+
+    // WHEN
+    const newTemplate = {
+      Resources: {
+        ServerlessFunction: {
+          Type: 'AWS::Serverless::Function',
+          Properties: {
+            CodeUri: 's3://bermuda-triangle-1337-bucket/new-handler.zip',
+          },
+        },
+      },
+    };
+
+    let differences = fullDiff(currentTemplate, newTemplate, {
+      Changes: [
+        {
+          Type: 'Resource',
+          ResourceChange: {
+            Action: 'Modify',
+            LogicalResourceId: 'ServerlessFunction',
+            ResourceType: 'AWS::Lambda::Function', // The SAM transform is applied before the changeset is created, so the changeset has a Lambda resource here!
+            Replacement: 'False',
+            Details: [{
+              Evaluation: 'Direct',
+              Target: {
+                Attribute: 'Properties',
+                Name: 'Code',
+                RequiresRecreation: 'Never',
+              },
+            }],
+          },
+        },
+      ],
+    });
+    expect(differences.resources.differenceCount).toBe(1);
+  });
+
   test('imports are respected for new stacks', async () => {
     // GIVEN
     const currentTemplate = {};