Registers one or more command sources. Each source becomes a multi entry
on CNGX_COMMAND_SOURCE; call provideCommands from several app parts
and injectCommands merges all of them.
Returns Provider[] (not EnvironmentProviders), so it registers at any
injector scope - app root, a lazy route, or a component's providers /
viewProviders - letting a route or component contribute a scoped command
set without reaching for the raw CNGX_COMMAND_SOURCE multi-provider.
// app rootbootstrapApplication(AppComponent, { providers: [provideCommands(fileCommands)] });// or component scope