Add UnwrapSyntaxNode action

[Gregoor]

Remake of #8967

Hey there,

I have started relying on this action, that I've also put into VSCode as an extension. On some level I don't know how people code (cope?) without it:

Release Notes:

• Added UnwrapSyntaxNode action

https://github.com/zed-industries/zed/assets/4051932/d74c98c0-96d8-4075-9b63-cea55bea42f6

Since I had to put it into Zed anyway to make it my daily driver, I thought I'd also check here if there's an interest in shipping it by default (that would ofc also personally make my life better, not having to maintain my personal fork and all).

If there is interest, I'd be happy to make any changes to make this more mergeable. Two TODOs on my mind are:

• unwrap multiple into single (e.g. fn(≤a≥, b) to fn(≤a≥))
• multi-cursor
• syntax awareness, i.e. only unwrap if it does not break syntax (I added a coarse version of that for my VSC extension)

Somewhat off-topic: I was happy to see that you're also using rare special chars in test code to denote cursor positions.

Release Notes:

• Added UnwrapSyntaxNode action