This mirrors VSCode setting that inspired `snippet_sort_order` to begin
with; VSCode supports inline/top/bottom/none, with none completely
disabling snippet completion. See
https://code.visualstudio.com/docs/editing/intellisense#_snippets-in-suggestions

This is helpful for LSPs that do not allow configuring snippets via
configuration such as clangd.

Release Notes:

- Added `none` as one of the values for `snippet_sort_order` to
completely disable snippet completion.