aggressive reparenting of trailing delimiter after cut

[disconcision]

Not sure if this is a bug, but definitely an interesting source of possible confusion. Given:

Cutting produces:

this occurred during ER's task 4; they had already felt they had stubbed out a separate dist definition at the top with an empty definition, and were going to move content to the definition. but after the cut, the orphan in in the body of the fun gets reparented to the new let, which then makes the fun part of the new let's definition

[disconcision]

Here's another example from EE2, that was sort of serendipitous but also surprising:

given:

cutting yields:

so you end up in the hole that you wanted to fill and can just paste