Core: Fix React peer dependency warnings

[JReinhold]

Closes #25072

What I did

Fixed a handful of peer dependency warnings where React was requested in the dependency chain but not "officially" present.

• Addons backgrounds, interactions, measure and outline: Moved @storybook/icons to a devDependency because it's already globalized in the manager.
• Addon-docs: Added @types/react as a regular dependency to satisfy @mdx-js/react peer dependency
• Theming and blocks: Made peer dependency on React optional. It's not needed when used in the manager or in addon-docs, which is 99 % of use cases. Some projects use @storybook/theming in the wild which needs the React peer dep still. Theoretically, using @storybook/blocks outside of Storybook could also be valid and in those cases it need to peer dep on React still.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

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>