Introducing BertForMultipleChoice transformer

[danilojsl]

Description

This PR adds the BertForMultipleChoice model, extending the BERT architecture to handle multiple-choice tasks.

Motivation and Context

This transformer enhances BERT’s versatility by allowing users to tackle tasks that involve multiple-choice scenarios, such as:

• Standardized test questions
• Survey or quiz automation

How Has This Been Tested?

Screenshots (if appropriate):

• Local Tests
• Google Colab notebooks

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Code improvements with no or little impact
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING page.
• I have added tests to cover my changes.
• All new and existing tests passed.