feat(typescript): extract extend global types to its own section

[ArmandPhilippot]

Description (required)

• Adds a new "Extending global types" section in guides/typescript.mdx:

  • move Extending windows & globalThis as a subheading
  • create a Add non-standard attributes subheading and move a part of Built-in HTML attributes in it
  • create a new Using imports subheading (and its contents) to hopefully solve Update documentation on 'Middleware types' #11759 and all the similar issues we had

• Removes a duplicated link in "Import Aliases" (which I found confusing as a user and I don't think this is great for screen readers as well)

• Updates pages mentioning .d.ts files to add direct or indirect linking (when the environment variable guide might be more appropriate) to the new Typescript guide section.
  I used ReadMore links for the CMS guides but I noticed we lack of consistency here: when linking to the environment variables page, some use :::note, some use :::tip and only a few use ReadMore. 😅

Related issues & labels (optional)

• Closes Extract JSX augmentation to its own section #12349, Update documentation on 'Middleware types' #11759
• Suggested label: add new content, improve or update documentation

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en/guides/cms/builderio.mdx	Source changed, localizations will be marked as outdated.
en/guides/cms/datocms.mdx	Source changed, localizations will be marked as outdated.
en/guides/cms/strapi.mdx	Source changed, localizations will be marked as outdated.
en/guides/environment-variables.mdx	Source changed, localizations will be marked as outdated.
en/guides/integrations-guide/alpinejs.mdx	Source changed, localizations will be marked as outdated.
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en/guides/integrations-guide/vercel.mdx	Source changed, localizations will be marked as outdated.
en/guides/middleware.mdx	Source changed, localizations will be marked as outdated.
en/guides/sessions.mdx	Source changed, localizations will be marked as outdated.
en/guides/typescript.mdx	Source changed, localizations will be marked as outdated.

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[sarah11918]

This looks like a really nice improvement! 🎉