feat(editor): Partial stroke eraser

[personalizedrefrigerator]

To-do

• [x] Allow switching between partial and full stroke erasers
• [x] Improve case for filled strokes (currently works, but not well)
• [x] Improve case where strokes to be erased are larger than the eraser head
• [x] Decimal trimming for split curves
• [ ] Add more tests
  • [x] At least one eraser integration test
  • [ ] Tests for Stroke.dividedBy
• [x] Remove instanceof Stroke test used to get stroke width within Eraser.ts — the eraser shouldn't need to know about stroke width.

Optional to-do (follow-up?)

• [ ] Partial erasing of images.

Screen recording

partial-stroke-erase.webm

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 7a244e8):

https://js-draw--pr63-work-stroke-eraser-i8b195vi.web.app

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