chore: hide and ignore lingering "main" assets

[rubencarvalho]

Description

This PR adds configuration to hide the main workspace folders (packages/, projects/, tools/, test/) from the IDE file explorer and gitignore.

Motivation and context

This helps reduce clutter in the IDE when switching between main and barebones work, as these top-level directories contain thousands of files that can make navigation difficult.

Author's checklist

• I have read the CONTRIBUTING and PULL_REQUESTS documents.
• I have reviewed at the Accessibility Practices for this feature, see: Aria Practices
• I have added automated tests to cover my changes.
• I have included a well-written changeset if my change needs to be published.
• I have included updated documentation if my change required it.

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Reviewer's checklist

• Includes a Github Issue with appropriate flag or Jira ticket number without a link
• Includes thoughtfully written changeset if changes suggested include patch, minor, or major features
• Automated tests cover all use cases and follow best practices for writing
• Validated on all supported browsers
• All VRTs are approved before the author can update Golden Hash

Manual review test cases

• _checkout main, run yarn build checkout ruben/hide-main-folders. There should be no lingering files.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 11b134b

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[github-actions]

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When a visual regression test fails (or has previously failed while working on this branch), its results can be found in the following URLs:

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Deployed to Azure Blob Storage: pr-5827

If the changes are expected, update the current_golden_images_cache hash in the circleci config to accept the new images. Instructions are included in that file.
If the changes are unexpected, you can investigate the cause of the differences and update the code accordingly.

[github-actions]

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