Fixes#7487.
`KMN_API` defines only import/export/static modifiers for functions, so
it makes no sense to apply it to a typedef. (Previously, I thought it
also included a calling convention, but it doesn't.)
Adds infrastructure required to support caps lock control on keyboard
activation per #5822.
Keyboardprocessor implementation is currently a stub, and engines will
need corresponding updates to support the new API.