This introduces NIR, but only as an accepting grammar; it doesn't yet emit
the NIR IR, beyond TODOs.
This modifies `tamec` to, while copying XIR, also attempt to lower NIR to
produce parser errors, if any. It does not yet fail compilation, as I just
want to be cautious and observe that everything's working properly for a
little while as people use it, before I potentially break builds.
This is the culmination of months of supporting effort. The NIR grammar is
derived from our existing TAME sources internally, which I use for now as a
test case until I introduce test cases directly into TAMER later on (I'd do
it now, if I hadn't spent so much time on this; I'll start introducing tests
as I begin emitting NIR tokens). This is capable of fully parsing our
largest system with >900 packages, as well as `core`.
`tamec`'s lowering is a mess; that'll be cleaned up in future commits. The
same can be said about `tameld`.
NIR's grammar has some initial documentation, but this will improve over
time as well.
The generated docs still need some improvement, too, especially with
generated identifiers; I just want to get this out here for testing.
DEV-7145
Mike Gerwitz