Docs: Updates for 8.2 features

[kylegach]

What I did

Changes from #28452 & #28444, targeting main

Checklist for Contributors

Testing

N/A

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

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[greptile-apps]

PR Summary

• Updated error message in code/core/src/preview-errors.ts for MountMustBeDestructuredError
• Added docs/_snippets/before-all-in-preview.md and docs/_snippets/before-each-in-preview.md for initialization and MockDate usage
• Improved snapshot testing in docs/_snippets/button-snapshot-test-portable-stories.md and docs/_snippets/component-test-with-testing-library.md
• Added advanced usage examples in docs/_snippets/mount-advanced.md and docs/_snippets/mount-basic.md
• Removed outdated snippets docs/_snippets/portable-stories-import-annotations.md and docs/_snippets/portable-stories-jest-with-loaders.md

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