Rust: split match arms into blocks about treesj

[Wansmer]

I am planning to implement this feature in the future. (It looks simple, but require some structural changes to finding nodes to split/join).

If you have another examples for this case in another languages – please send – it will help.

I was planning to implement this myself and submit a PR, but from what I looked, this plugin only has support for splitting nodes with clear delimiters. So I became unsure to how to implement it.

This plugin build yet one tree around treesitter tree. It means, that you can add new nodes with any content in any tree branch. In case x => { x; } to x => x;, first need to implement finding node by tsnode:field(). At the moment, finding only by tsnode:type().

[Wansmer]

Done at #77