refactor: specify type at bbox

[nayounsang]

Describe what your pull request does. If you can, add GIFs or images showing the before and after of your change.
I found that bbox's type is any.
Bbox is let variable, so I thought it would be good to improve.

Change type

• bugfix
• improvement
• feature
• api
• other

Test plan

1. yarn run test

• Just I change the type, so logic is not changed. It just checks to see if there are any type errors.

• Unit tests

• End to end tests

Release notes

• When I see the code in packages/editor/src/lib/exports/getSvgJsx.tsx, Improvements were found.

// L57
let bbox: = null // any type

• This is declared as let, but it is any type.
• I felt this was a risk for future maintenance.
• So I specify the type of bbox.

let bbox: null | Box = null

[vercel]

@nayounsang is attempting to deploy a commit to the tldraw Team on Vercel.

A member of the Team first needs to authorize it.

[steveruizok]

Thanks @nayounsang !