Add debug lens for rebar3 projects

Summary: Return a code lens associated to the `debugSingle` command, so that it can be used to start a debugging session from the IDE.

Reviewed By: alanz

Differential Revision: D68200393

fbshipit-source-id: 89929b4e846f692c773e4cb0fd7f6a2e93e6841a

crates/elp/src/to_proto.rs

@@ -737,6 +737,14 @@ pub(crate) fn code_lens(
                             data: None,
                         });
                     }
+                    if lens_config.debug {
+                        let debug_command = command::debug_single(&r, debug_title);
+                        acc.push(lsp_types::CodeLens {
+                            range: annotation_range,
+                            command: Some(debug_command),
+                            data: None,
+                        });
+                    }
                 }
                 ProjectBuildData::Static(_) => {}
                 ProjectBuildData::Otp => {}