Fixes https://github.com/zed-industries/zed/issues/8020
 
This PR adds a new shortcut cmd-right, if a copilot suggestion exists.
The suggestions is accepted word by word.
It emulates the behaviour of VS Code's Github Copilot implementation.


Release Notes:

- Added ability to accept partial copilot suggestions ([8020](https://github.com/zed-industries/zed/issues/8020))