Support transpiling modules into main deployment

Currently modules are transpiled into nested deployments. It would be nice if there was an option to instead transpile modules straight into the parent deployment. For example, if I have a Bicep file that creates a SQL server and a module to create two databases, it'd be nice if the JSON template contained all three resources without a nested deployment.

This would help with a few things:
- Nested deployments aren't super intuitive, and Bicep modules will be increasing their usage.
- Modules can increase the overall time of deployments, because the nested deployment won't complete until all of its resources have finished deploying. If the resources were all moved to the root deployment, ARM could schedule the individual resource deployments based purely on their specific dependency list.

I know this is likely to be difficult and have lots of edge cases - I'm curious if this is something you've thought about though.