The TypeRef name comes from IntelliJ days, where you often have both
type *syntax* as well as *semantical* representation of types in
scope. And naming both Type is confusing.
In rust-analyzer however, we use ast types as `ast::Type`, and have
many more semantic counterparts to ast types, so avoiding name clash
here is just confusing.
The primary advantage of ungrammar is that it (eventually) allows one
to describe concrete syntax tree structure -- with alternatives and
specific sequence of tokens & nodes.
That should be re-usable for:
* generate `make` calls
* Rust reference
* Hypothetical parser's evented API
We loose doc comments for the time being unfortunately. I don't think
we should add support for doc comments to ungrammar -- they'll make
grammar file hard to read. We might supply docs as out-of band info,
or maybe just via a reference, but we'll think about that once things
are no longer in flux
