It doesn't seem editor agnostic to me. It seems geared towards vscode.
The idea is also not new - python has had docstrings since the 90s. They never thought to show the full definition on hover or autocomplete, probably because it's noise most of the time, but a lot of people seem to like it.
With that, any editor that supports Language Servers can use those to provide better support to a language without implementing any details.
In this case, you can see some of the supported editors in the README itself: https://github.com/bash-lsp/bash-language-server#clients