feat: Merge ErrorLoad and Load, make Input and Output typings public

[elliott-with-the-longest-name-on-github]

Merged the declarations of ErrorLoad and Load and their corresponding input types ErrorLoadInput and LoadInput. Moved the LoadInput and LoadOutput interfaces to index.d.ts from private.d.ts.

No behaviors have actually been changed, but the status and error properties are now part of the official public API.

See issue #4461 for discussion.

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[changeset-bot]

🦋 Changeset detected

Latest commit: b34fa52

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

This PR includes changesets to release 1 package

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@sveltejs/kit	Patch

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[Rich-Harris]

Thank you!