[feature] ROS Launch Debugger & substituteVariables Support

[seanyen]

In vscode, there is a AbstractVariableResolverService to help dynamically generate launch\attach request at runtime by using abstract variables. For example, ${file} is replaced by the active open file path. This ability enables that developers can define a generic ROS launch task and simply go to the editor to open roslaunch file and press F5 to debug.

BTW, currently we hooked our logic on the resolveDebugConfiguration and the code path didn't get a chance to run AbstractVariableResolverService for the variables resolving.

https://github.com/microsoft/vscode/blob/4c45266943228286126e1ad9f840851a0cde594d/src/vs/workbench/contrib/debug/browser/debugService.ts#L369

[kejxu]

good point! VS Code variables get resolved when they are passed to the debug adapter, not sure how to resolve those inside an extension's context.

some relevant ticket to vscode repo: microsoft/vscode#79518