We have fields where the field editor type is set to either “select input” or “radio group” (or where the visual select plugin is used – though for this discussion, let’s focus on DatoCMS’s core functionality 
).
Is it possible to generate a type that includes all the possible values defined for such a field?
I don’t believe so, sorry 
The typedefs are usually generated from your schema, not your values. But you can use the CMA to pull the validation rules for that field (the enum validator at https://www.datocms.com/docs/content-management-api/resources/field#validators) and then write a script to generate a typedef from it?