Do not show `Extract Variable` refactor as available, if the selection range is empty

[paracycle]

Currently the Ruby LSP shows a persistent light-bulb in VSCode as if Refactor: Extract Variable was always available. My guess is that this is because we also consider an empty selection as a valid selection and offer extracting variable as an option.

Extract Variable should only be available when a meaningful selection is performed.

Ref: https://www.reddit.com/r/ruby/comments/124vb7i/comment/je1fryk/?utm_source=reddit&utm_medium=web2x&context=3