chore: correct 1.0 changesets

[QuentinRoy]

Summary

• classify consumer-facing breaking changes as major for the 1.0 release
• add missing compatibility notes found by comparing against v0.10.1
• clarify ID and ESM migrations and classify the internal RxJS import change as patch
• support RxJS 7.2 and newer, the first 7.x release with root operator exports
• fix the README CDN example to target the 1.x API

Validation

• yarn test
• yarn typecheck
• yarn build
• yarn lint (3 existing warnings, no errors)
• yarn prettier --check .changeset README.md
• yarn changeset status
• runtime tests and production build against RxJS 7.2.0

[changeset-bot]

🦋 Changeset detected

Latest commit: b146bdf

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
marking-menu	Major

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