Improve output of tree-sitter-subtree

[zetashift]

Describe your feature request

Current output of :tree-sitter-subtree

This reads fine for small code snippets, but for big blocks it gets kind of unreadable.
A way of improving this, from the-mikedavis from helix Matrix chat:

we could format these like tree-sitter parse pretty easily, i.e. break lines and do indentation

[fisherdarling]

I'll work on this :) I think I have a pretty simple implementation.