### Issue # (if applicable) Closes #31170. ### Reason for this change CodeBuild recently added support for Mac builds. https://aws.amazon.com/about-aws/whats-new/2024/08/aws-codebuild-mac-builds/ The CDK can to be extended to support Mac CodeBuild fleets, as well as using those fleets in CodeBuild projects. ### Description of changes - Added `MAC_ARM` value to EnvironmentType [enum](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-codebuild/lib/environment-type.ts) - Added `MacBuildImage` to [project.ts](https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-codebuild/lib/project.ts) All design decisions were made by following the previous precedent set by `LinuxBuildImage` and `WindowsBuildImage`. ### Description of how you validated changes I added unit tests and integration tests for `MacBuildImage`. I ensured that the CDK was able to build, and that the output CloudFormation stack had the correct resources. I also successfully built the Codebuild project that was deployed. ### 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* --------- Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>