With the new work on bindings, we no longer need to keep any arrows
stuff hard-coded in `editor`, so let's move it to `tldraw` with the rest
of the shapes.
Couple other changes as part of this:
- We had two different types of `WeakMap` backed cache, but we now only
have one
- There's a new free-standing version of `createComputedCache` that
doesn't need access to the editor/store in order to create the cache.
instead, it returns a `{get(editor, id)}` object and instantiates the
cache on a per-editor basis for each call.
- Fixed a bug in `createSelectedComputedCache` where the selector
derivation would get re-created on every call to `get`
### Change Type
- [x] `sdk` — Changes the tldraw SDK
- [x] `improvement` — Improving existing features
### Release Notes
#### Breaking changes
- `editor.getArrowInfo(shape)` has been replaced with
`getArrowInfo(editor, shape)`
- `editor.getArrowsBoundTo(shape)` has been removed. Instead, use
`editor.getBindingsToShape(shape, 'arrow')` and follow the `fromId` of
each binding to the corresponding arrow shape
- These types have moved from `@tldraw/editor` to `tldraw`:
- `TLArcInfo`
- `TLArrowInfo`
- `TLArrowPoint`
- `WeakMapCache` has been removed
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