Expose treesitter and language packages to plugins

[jonathanmorley]

I am trying to implement a filter that would be able to detect comment-only changes.

It would be useful to have access to tree-sitter to analyze the files involved in the PR (and do some similar operations to isFormattingChange.

This could allow users to solve https://github.com/linear-b/gitstream/issues/482 themselves too.

https://www.npmjs.com/package/tree-sitter https://www.npmjs.com/search?q=keywords:tree-sitter