feat(debugger): debug Ruby programs and tests with rdbg (#2173)

Ruby files, `rails server`, Rake tasks, RSpec and Minitest configurations
can be debugged with rdbg, using the project's Ruby. In a Bundler project
it runs through the bundle; if the bundle lacks the `debug` gem, debugging
stops with an error asking to add `gem "debug"` to the Gemfile.

languages/ruby.toml

@@ -23,3 +23,10 @@ command = "solargraph"
 args = ["stdio"]
 root-markers = ["Gemfile", ".solargraph.yml"]
 install-hint = "gem install solargraph"
+
+[debugger]
+adapter = "rdbg"
+command = "rdbg"
+args = ["-O", "--port", "${port}", "-c"]
+transport = "tcp"
+install-hint = "gem install debug"