Add an option to make paste at cursor the default.
Not sure if we also want to expose this on tldraw.com? For now I did,
but happy to remove if we'd want to keep the preferences simple.
We could also add this to the `TldrawOptions`, but it felt like some
apps might actually allow this customization on a per user level.
Solves https://github.com/tldraw/tldraw/issues/4066
### Change type
- [ ] `bugfix`
- [ ] `improvement`
- [x] `feature`
- [ ] `api`
- [ ] `other`
### Test plan
1. Copy / pasting should still work as it works now: `⌘ + v` pastes on
top of the shape, `⌘ + ⇧ + v` pastes at cursor.
2. There's now a new option under Preferences to paste at cursor. This
just swaps the logic between the two shortcuts: `⌘ + v` then pastes at
cursor and `⌘ + ⇧ + v` pastes on top of the shape.
### Release notes
- Allow users and sdk users to make pasting at the cursor a default
instead of only being available with `⌘ + ⇧ + v`.
a85c215ffc