This is the beginning of static symbols, which is becoming increasing
necessary as it's quite a pain to have to deal with interning static strings
any place they're used.
It's _more_ of a pain to do that in conjunction with newtypes (e.g. `QName`,
`AttValue`, etc) that make use of `SymbolId`; this will allow us to
construct _those_ statically as well, and additional work to support that
will be coming up.
DEV-10701
This is an initial implementation optimized for expected use
cases. Hopefully that pans out and doesn't come back to bite me.
Regarding the context: it only allows for interned paths atm, which are
strings (and so much be valid UTF-8, which is fine for us, but sucks for
something more general-purpose). I'll be curious if the context needs
extension later on, or if different contexts will be stored in IRs (e.g. to
store a template application site as well as the location of the expansion
within the template body).
This begins to introduce the ASG, backed by Petgraph. The API will continue
to evolve, and Petgraph will likely be encapsulated so that our
implementation can vary independently from it (or even remove it in the
future).
Mike Gerwitz