feat(codebuild): support three arm-based compute types, Medium, X-Lar…

…ge and 2X-Large (#31214)

### Issue # (if applicable)

Closes #30869.

### Reason for this change
Because three new arm-based compute types have become supported due to an update.

Announcement: [AWS CodeBuild now supports three new Arm-based compute types
](https://aws.amazon.com/about-aws/whats-new/2024/08/aws-codebuild-three-arm-based-compute-types/)

### Description of changes
Modify the validate method to allow Medium, X-Large, and 2X-Large as Arm-based compute types.



### Description of how you validated changes
Modify unit tests and integ tests.



### 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)

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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*