Remove `MarkdownEditor` and related code

[iansan5653]

Closes #3604

Removes the MarkdownEditor and related components and hooks. I also reviewed our dependencies and removed any that were only used by this code. Not much to say here - it was mostly just deleting everything and running npm i.

Changelog

Removed

Deprecated experimental components and hooks:

• MarkdownEditor
• MarkdownViewer
• InlineAutocomplete
• useCombobox
• useDynamicTextareaHeight
• useIgnoreKeyboardActionsWhileComposing
• useSafeAsyncCallback
• useSyntheticChange
• useUnifiedFileSelect

Rollout strategy

• [ ] Patch release
• [ ] Minor release
• [x] Major release; if selected, include a written rollout or migration plan
• [ ] None; if selected, include a brief description as to why

Rollout for GitHub will be straightforward for this change as all internal code has already migrated to the internal versions of these components and hooks.

[!NOTE] Although this is all experimental code and we can delete it at any time since experimental code doesn't follow semver, I think it's more polite to any downstream consumers to delete this in a major version, giving this change more visibility. There's no rush to make this change as the code is already deprecated, so we can hold off merging this until we're ready to make another major bump (or we can merge to a release branch if we have one).

Merge checklist

• [x] Added/updated tests
• [x] Added/updated documentation
• [x] Added/updated previews (Storybook)
• [x] Changes are SSR compatible
• NA: ~~[ ] Tested in Chrome~~
• NA: ~~[ ] Tested in Firefox~~
• NA: ~~[ ] Tested in Safari~~
• NA: ~~[ ] Tested in Edge~~
• [ ] (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 32d4761096faba6d9df6bff634cb0943c3d28ca8

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

This PR includes changesets to release 1 package

Name	Type
@primer/react	Major

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[github-actions[bot]]

size-limit report 📦

Path	Size
dist/browser.esm.js	105.97 KB (0%)
dist/browser.umd.js	106.66 KB (0%)

[github-actions[bot]]

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