lsp: notify client when config file is auto-discovered

[kitsonk]

In order to be able to provide "auto-enablement" of Deno projects with the language server when a config file is auto-discovered, the language server would need to search the workspace and notify the client when a deno.jsonc file is auto-discovered as well as have semantics for being "enabled" when that occurs (but respecting explicit configuration of not-being enabled).

The biggest challenge is the explicit enablement/disablement, as we can't really disambiguate that at the moment. The specific case which I don't think we can currently handle is that there is a deno.jsonc in the workspace root, but the user has for whatever reason, explicitly set it as "deno.enable": false versus that being the default value.

Ref: denoland/vscode_deno#617

[nayeemrmn]

Closed by #20827.