This PR adds some functionality for turning shapes into images.
It adds:
- the `flattenShapesToImages`
- the `useFlatten` hook
- a `flatten-shapes-to-images` action (shift + f)
- adds `flattenImageBoundsExpand` option
- adds `flattenImageBoundsPadding` option
## Flatten shapes to images
The `flattenShapesToImages` helper method will 1) create an image for
the given shape ids, 2) add it to the canvas in the same location / size
as the source shapes, and then 3) delete the original shapes. The new
image will be placed correctly in the z index and in the correct
rotation of the root-most ancestor of the given shape ids.
It has an argument, `flattenImageBoundsExpand`, which if provided will
chunk the given shapes into images based on their overlapping (expanded)
bounding boxes.
By default, the flatten action uses the editor's
`options.flattenImageBoundsExpand`. The `flattenImageBoundsPadding`
option is used as a value for how much larger the image should be than
the source image bounds (to account for large strokes, for example).
### Change Type
- [x] `sdk` — Changes the tldraw SDK
- [x] `feature` — New feature
### Test Plan
1. Select shapes
2. Select context menu > edit > flatten
- [ ] Unit Tests
- [ ] End to end tests
### Release Notes
- Add Flatten, a new menu item to flatten shapes into images
5bf05bbb3c