The only way to start a debug session in vscode is by populating the launch.json content. In the 'live share' extension the launhc.json is not the only source of debug configuartions, for example when connected to a VS host there will be no launch.json file. Also live share will artificially create all the 'shared debug configurations' available on runtime without the need to change the content of launch.json.

a simple way to achieve is by something like this:

interface DebugLaunchConfigrationsProvider {
 getLaunchConfigurations(): ProviderResult<DebugConfiguration[]>;

onLaunchConfigurationsChanged: Event;
}