[Workers] Document missing ReadableStream APIs

[Nic-Polumeyv]

Summary

Documents the ReadableStream APIs the runtime ships but this page omits. Prompted by sveltejs/kit#16622, where the gap led a maintainer to assume ReadableStream.from does not exist on Workers.

The tee() entry sticks to user-facing behavior, per the review feedback on #10026.

Fixes #9285

Documentation checklist

• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.

[cloudflare-docs-bot]

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