WIP: Routes autocomplete

[andyw8]

I don't think there's any need to cache routes, since even on Core, withover 5000 routes, it takes only 1ms:

shopify(dev)> start=Time.now; Rails.application.routes.named_routes.helper_names.to_a; Time.now-start
=> 0.001078413

TODO:

• cache routes, and reload if routes.rb changes?
• don't return results if app is using Sorbet
• support for routes in engines (see here for ideas)
• kind, documentation
• disable/enable based on class type (similar approach to Use ancestors to determine test framework in code lens ruby-lsp#1334)