Fix for #1835: Allow giving a custom name to keywords implemented using ...

...the static and the hybrid APIs
I think it would be better to expose the decorator via `robot.api`. `robot.utils` is for utilities needed by Robot itself that can also be used by external libraries/tools, and `robot.api` for stuff only used externally. This decorator is in the latter category.

I'm not entirely sure how to expose this under `robot.api`, though. Should we expose it directly as `robot.api.keyword` or should we rather have a separate module for decorators? The latter would probably be a better idea because then it could contain also this currently still work-in-progress decorator for argument type validation and conversion: https://github.com/pekkaklarck/argtypesThis is actually something I think is better to resolve outside this pull request.