Feature request: Make `fs_map` work with UnixDomainServer

[jvilk-stripe]

Your proposal
Make fs_map work with UnixDomainServer. Right now, the code disables this feature for UnixDomainServer:

https://github.com/ruby/debug/blob/master/lib/debug/server_dap.rb#L131

Additional context

Stripe runs ruby on a remote server and VS Code on a laptop. We proxy the unix domain socket from server to laptop, and need to use the fs map feature to translate file paths.

[ko1]

Maybe #745 fixes it.