This diff mostly adds an image annotator example, but also has a couple
of drive-by changes:
- Added a 'use-cases' category to the examples app for this style of
mini-app
- Add `editor.pageToViewport`, which is like `editor.pageToScreen` but
works with viewport coordinates (better for `InFrontOfTheCanvas` stuff)
- Prevent the chrome side-swipe-to-go-back thing in the examples app
Some cool features of the image annotator:
- The image cannot be unlocked, and cannot have shapes places behind it
- I still need to work out a way of removing the context menu though
- Anything you place outside the bounds of the image (and therefore
outside the bounds of the export) will be greyed out
- You can't change pages
- unless you find the "move to page" action... need to fix that
- The camera is constrained! It'll keep the image roughly centered on
the screen. If you pick a very long thin image, you can only scroll
vertically. If you pick a very big one, it'll default it to a reasonable
size.
### Change Type
<!-- ❗ Please select a 'Scope' label ❗️ -->
- [x] `sdk` — Changes the tldraw SDK
- [x] `docs` — Changes to the documentation, examples, or templates.
<!-- ❗ Please select a 'Type' label ❗️ -->
- [x] `feature` — New feature
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