auto merge of #10891 : chris-morgan/rust/macroize-(or-should-that-be-…

…macroify)-syntax--parse--token-so-that-we-don't-make-mistakes-and-to-reduce-the-maintenance-burden, r=huonw

I also renumbered things at the same time; ``in`` was shifted into its
alphabetical position and the reserved keywords were reordered (a couple
of them were out of order).

Unused special identifiers are also removed in the second part.