Support for extensions that rely on robotframework-pythoncore

[takeda]

There is a library that allows to bigger extension to be split into smaller pieces:
https://github.com/robotframework/PythonLibCore

It looks like this plugin doesn't understand sub-libraries, so it shows keywords from them as errors.

[jnhyperion]

It's because the sub libraries are loaded dynamically in robot runtime. In this case, the library should provide a pyi file to enable IDE to parse the method signatures.

For example:
SeleniumLibrary

and it's pyi file:
__init__.pyi