refactor: `<TodoSliceComponent />`

[lihbr]

Types of changes

• [ ] Chore (a non-breaking change which is related to package maintenance)
• [x] Bug fix (a non-breaking change which fixes an issue)
• [ ] New feature (a non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Description

Mapped slices would cause the <TODOSliceComponent /> component to throw because of a different interface used by mapped slices (slice type being top level instead of nested under the slice property).

This standardizes the props given to <TODOSliceComponent /> so everything keeps working smoothly based on our Svelte implementation: https://github.com/prismicio/prismic-svelte/blob/master/src/SliceZone/SliceZone.svelte#L118-L128

I first explored adapting the <TODOSliceComponent /> to support different interfaces instead, but it resulted in messier code in my opinion: https://github.com/prismicio/prismic-vue/blob/95d5771b51dc45df5bd6663178afceae8942dc4c/src/components/SliceZone.ts#L263-L280

Checklist:

• [ ] My change requires an update to the official documentation.
• [x] All TSDoc comments are up-to-date and new ones have been added where necessary.
• [x] All new and existing tests are passing.