Extend codegen to allow simple typedefs

[quietust]

Dwarf Fortress's code makes use of a wide variety of simple integer typedefs: for example, there's typedef int16_t LocalPos; for local map coordinates, typedef uint16_t Temperature; for (Urist-scaled) temperature values, and typedef int32_t MatGloss; for materials that need to reference creatures, plants, or histfigs.

Historically, some of these have changed - notably, MatGloss changed from int16_t to int32_t between 0.28.181.40d and 0.31.01, and AppearanceModifierValue (used in body/bp appearance modifiers as well as hair length styles) changed from int16_t to int32_t at some point between 0.31.25 and the current version. Being able to reference these types by name could potentially make it easier to consume future structure updates, and it could potentially also make it easier to see what kind of data is stored in a field (if its name happens to be unclear).