Support edit prediction

[keirlawson]

Models such as Zed's Zeta2 or https://www.inceptionlabs.ai/blog/introducing-mercury-edit-2 support predicting next edits not just at the cursor but potentially elsewhere in the document. This would be nice functionality to have however so far as I can see there isn't a portion of the LSP spec that supports this functionality. VIM plugin: https://github.com/cursortab/cursortab.nvim