feat(mixins-preview): add auto-generated L1 property mixins

[mrgrain]

Reason for this change

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

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:

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

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[aws-cdk-automation]

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