feat: AI autocomplete [render preview]

[YousefED]

Summary

The AI Autocomplete extension provides real-time, AI-powered text completion suggestions as users type. When enabled, the editor will display inline suggestions that can be accepted with the Tab key or dismissed with Escape.

Rationale

This feature helps users to get automatic AI generated suggestions based on the current context.

Changes

• An API endpoint has been added here: https://github.com/TypeCellOS/BlockNote/pull/2191/files#diff-17c91c67f28aa1ed975bff4586bdbcd87164a3688342272b581ec712949d7d15
• The AI example has been extended here: https://github.com/TypeCellOS/BlockNote/pull/2191/files#diff-9ebfeb550917300e498ffaa17f4360d2a9a53b6e654ee6ed76ecbddeff1a7940
• The AutoComplete extension has been added: https://github.com/TypeCellOS/BlockNote/pull/2191/files#diff-1012946af8cf61494dcd571394754f8f3609299bdc700cf8901d09eba7958eaa

Impact

Testing

Manual and unit tests

Screenshots/Video

Demo: https://blocknote-git-feature-ai-autocomplete-typecell.vercel.app/ai/minimal

https://github.com/user-attachments/assets/1113eb66-6d82-4e7d-941e-d3ff41d73253

Checklist

• [x] Code follows the project's coding standards.
• [x] Unit tests covering the new feature have been added.
• [x] All existing tests pass.
• [x] The documentation has been updated to reflect the new feature

Additional Notes

Consider this an early draft, we're still working out the API and UX