feat: 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.

It should be possible to access a built version of the PDF editor example here.

To-do

• Fix exported text bounding box.
• 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?.
• 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]

Visit the preview URL for this PR (updated for commit 5661b19):

https://js-draw--pr67-work-pdf-support-9v0zw3ml.web.app

_{(expires Mon, 13 Jan 2025 10:46:32 GMT)}

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_{Sign: e560ee6f7bb6b79cb55b42fb4c05e9fd1b5c506e}

[personalizedrefrigerator]

Direct link to example: https://js-draw--pr67-work-pdf-support-9v0zw3ml.web.app/examples/example-pdf/example.html

[personalizedrefrigerator]

Closing for now. This pull request (or a similar one with a different approach) may be re-opened in the future.