Add Skia Gold support to flutter/packages for golden file testing #172933

This issue tracks the work to integrate Skia Gold for golden file testing in the flutter/packages repository CI.

As we relocate the material and cupertino libraries (#101479), we must preserve their extensive golden file tests. Integrating with Skia Gold is critical for preventing visual regressions in these packages and ensuring their visual fidelity remains high.

• The CI for flutter/packages will need to authenticate with and upload results to Skia Gold, and utilize goldctl as a dependency
• Golden file tests from the relocated material and cupertino packages should run successfully in the new environment.
• Contributors should be able to triage and approve golden file changes for pull requests in this repository through the Skia Gold dashboard.

Ideally we would set this up and use a package already in flutter/packages to ensure everything is working before moving material and cupertino over.