Implement Index Buffering

[jjsheets]

Description

Changed input data to provide an index buffer in addition to the vertex buffer. Implemented mocking needed for new functions used. Implemented code needed to provide the index buffer to Vulkan.

Checklist

• [x] Reference the issue this PR fixes: #71
• [x] Create tests which fail without the changes (if possible/relevant)
• [x] Verify the code compiles correctly
• [x] Verify all tests passing
• [x] Add yourself/the copyright holder to the AUTHORS.md file
• [x] Verify the changes are licensed compatible to the LGPL-2.1 License

[github-actions[bot]]

• Verify all tests pass in CI
• If related to graphics or platform specifics, run tests manually on all supported OSes
• If PR is based on an issue, verify it fulfills the requirements of that issue