[Performance] Optimize copyDirectoryContents using glob cwd

[gonzaloriestra]

WHY are these changes introduced?

The copyDirectoryContents function used an absolute path with glob, followed by manual string replacement to calculate relative paths for the destination. This is less efficient and more error-prone than using the built-in cwd option in glob.

WHAT is this pull request doing?

• Updates copyDirectoryContents to use the cwd option in the glob call.
• Simplifies the relative path calculation by removing manual string stripping.
• Reduces memory overhead by working with relative paths during the globbing process.

How to test your changes?

Run the unit tests for cli-kit:
pnpm --filter @shopify/cli-kit vitest run src/public/node/fs.test.ts

Verification command:
pnpm nx lint cli-kit && pnpm nx type-check cli-kit

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 15242362493404967590 started by @gonzaloriestra

[google-labs-jules]

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