[Feature] Dragging area highlighting

[gracefh]

Highlighting to indicate which areas to drop object in to break relation

Steps (maybe):

• Potentially look at DefaultSelectionForeground and DefaultSelectionBackground components in TLDraw repo (idrk what exactly is going on here yet)
• TLdraw uses this tl-html-layer thing to transform the x coordinates if necessary -- we'll probably have to see how we can access that (or maybe we can just add it onto the html there?)
• We might need to start storing rotation information as well so that the selection looks right?