I'm used to provider's Provider.of() call to get a provider from elsewhere in the widget tree, but every Riverpod resource I've found relies on having access to the provider variable already (by having both widgets in the same file). For a provider that only reaches through two widgets, passing this variable is simple enough, but I don't see this being feasible for accessing providers that are created high up in the widget tree. Is there a proper way to get a provider?