Implemented `XLMRoberta` sub-tasks

[Seun-Ajayi]

Proposed changes

Implemented XLMRobertaForSequenceClassification, XLMRobertaForTokenClassification and XLMRobertaForQuestionAnswering and provided their corresponding tests. All tests passed.

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• [x] New Model Architecture
• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation Update (if none of the other choices apply)

[ToluClassics]

Sweet!

[ToluClassics]

Can you run install and run pre-commit on your files

[Seun-Ajayi]

Can you run install and run pre-commit on your files

Used autopep8 before now, would use pre-commit now

[Seun-Ajayi]

Ready to be Merged