most instances of this being used do not refer to the "current"
position, sometimes not even to one reasonably close by. it could also
be called `makePos` instead, but `at` seems clear in context.
(cherry picked from commit 835a6c7bcfd0b22acc16f31de5fc7bb650d52017)
Change-Id: I17cab8a6cc14cac5b64624431957bfcf04140809
ParserState better describes what this struct really is. the parser
really does modify its state (most notably position and symbol tables),
so calling it that rather than obliquely "data" (which implies being
input only) makes sense.
(cherry picked from commit 007605616477f4f0d8a0064c375b1d3cf6188ac5)
Change-Id: I92feaec796530e1d4d0f7d4fba924229591cea95
eldritch horrors