Support PDF annotation

[personalizedrefrigerator]

Summary

Adds support for PDF annotation through a new @js-draw/pdf-support package. This package exposes an interface that must be implemented for whichever PDF backend is to be used.

To-do

• [ ] Refactor MuPDF-related logic out of docs/examples/pdf-support and into a package that can be published to NPM.
  • Note: MuPDF is licensed under the GNU AGPLv3 — it will need to be made clear that this is the case in the package's README.
• [ ] Better page memory management.
  • [ ] Page images should be freed if not recently used.
  • [ ] Support caching pages at different zoom levels, perhaps by forcing the use of [js-draw's rendering cache?](https://github.com/personalizedrefrigerator/js-draw/blob/main/packages/js-draw/src/rendering/caching/RenderingCache.
• [ ] Support image annotations
• [ ] Support highlight annotations
• [ ] Support searching for PDF text
• [ ] (Optional/follow-up PR) Support selecting PDF text
• [ ] (Optional/follow-up PR) Support links
• [ ] (Optional/follow-up PR) Support form conrols
• [ ] (Optional) More memory-efficient saving of strokes.

[github-actions[bot]]

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