Idea: support un-wrapping

[PeterJCLaw]

It would be awesome if tuck knew how to un-wrap already wrapped code.

Probably we only want to un-wrap the specific part that is pointed to, however it may also be useful to have a mode which unwraps the whole line.

[PeterJCLaw]

Some WIP towards this in https://github.com/PeterJCLaw/tuck/tree/unwrap, which builds on https://github.com/PeterJCLaw/tuck/tree/generalise-edits.