chore(mixins-preview): typed L1 property mixins (#36062)

### Reason for this change

Adds auto-generated L1 property mixins for all CloudFormation resources, providing type-safe property application with merge strategies.

**Note:** Still a chore as package is still not yet released. This will come next.

### Description of changes

- Generates type-safe property mixins for every CloudFormation resource across all AWS services
- Adds package.json exports for all service-specific mixin modules (e.g., `@aws-cdk/mixins-preview/aws-s3/mixins`)
- Supports two merge strategies: MERGE (deep merge, default) and OVERWRITE (shallow assign)
- Enables applying L1 properties to both L1 and L2 constructs with full TypeScript support
- Updates README with L1 Property Mixins documentation and examples

Example usage:
```typescript
import '@aws-cdk/mixins-preview/with';
import { CfnBucketPropsMixin } from '@aws-cdk/mixins-preview/aws-s3/mixins';

const bucket = new s3.Bucket(scope, "Bucket")
  .with(new CfnBucketPropsMixin({
    versioningConfiguration: { status: "Enabled" },
    publicAccessBlockConfiguration: {
      blockPublicAcls: true,
      blockPublicPolicy: true
    }
  }));
```

### Describe any new or updated permissions being added

No new or updated IAM permissions.

### Description of how you validated changes

- Generated mixins for all AWS services
- Verified type safety and merge strategies
- Updated documentation with examples

### 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: mrgrain

packages/@aws-cdk/mixins-preview/.gitignore

@@ -20,3 +20,7 @@ junit.xml
 !**/*.snapshot/**/asset.*/*.d.ts
 
 !**/*.snapshot/**/asset.*/**
+
+# we ignore generated files that cannot contain hand-written info
+lib/services/*/index.ts
+lib/services/**/*.jsiirc.json

packages/@aws-cdk/mixins-preview/README.md

@@ -1,2 +1,3 @@
 export * as core from './core';
 export * as mixins from './mixins';
+export * from './services';

packages/@aws-cdk/mixins-preview/lib/index.ts

@@ -0,0 +1 @@
+export * from './ask.generated';

packages/@aws-cdk/mixins-preview/lib/services/alexa-ask/mixins.ts

@@ -0,0 +1 @@
+export * from './accessanalyzer.generated';

packages/@aws-cdk/mixins-preview/lib/services/aws-accessanalyzer/mixins.ts

@@ -0,0 +1 @@
+export * from './acmpca.generated';

packages/@aws-cdk/mixins-preview/lib/services/aws-acmpca/mixins.ts

@@ -0,0 +1 @@
+export * from './aiops.generated';

packages/@aws-cdk/mixins-preview/lib/services/aws-aiops/mixins.ts

@@ -0,0 +1 @@
+export * from './amazonmq.generated';

packages/@aws-cdk/mixins-preview/lib/services/aws-amazonmq/mixins.ts

@@ -0,0 +1 @@
+export * from './amplify.generated';

packages/@aws-cdk/mixins-preview/lib/services/aws-amplify/mixins.ts

@@ -0,0 +1 @@
+export * from './amplifyuibuilder.generated';