This will affect non-highlighting users of treesitter parsers, which vim.treesitter.{start,stop} until now did not (directly) affect.

I think this might be an opportunity to talk about how we want this API to look long-term. In this case, I would prefer that destroying a parser is controlled by an optional keyword (default tbd). @lewis6991 ?

We probably need some kind of registration mechanism so each application can keep a parser alive if it needs it.

The simplest method would be to require each application to hold a reference to the parser, and the internal table can be changed to hold weak references. That'll cause the parser to be automatically destroyed when necessary.