Cleanup @tldraw/ui types / exports (#1504)

This PR cleans up exports from TldrawUi, unifying types under `TLUi` and
removing many items from exports / marking others as internal.

### Change Type

- [x] `major` — Breaking Change

### Release Notes

- [editor] clean up / unify types

packages/ui/src/lib/components/StylePanel/StylePanel.tsx

@@ -13,7 +13,7 @@ interface StylePanelProps {
 	isMobile?: boolean
 }
 
-/** @public */
+/** @internal */
 export const StylePanel = function StylePanel({ isMobile }: StylePanelProps) {
 	const editor = useEditor()