Precise ASTs don’t support comments

[patrickt]

Ported from https://github.com/tree-sitter/haskell-tree-sitter/issues/99

In the a-la-carte AST world, we dealt with comments by reifying them as nodes in the AST; since ALC ASTs have a degree of heterogeneity w/r/t typing, this worked fine. In a precise AST world, we have no such luxury.

This is blocking us from writing any docstrings in precise tagging.