Search by dependencies

As a user, I would like to be able to search for construct libraries that have a particular dependency, such as @aws-cdk/aws-ec2.

This could require a different search mechanism since the current search we have available is limited to the information in `catalog.json`, which does not contain package dependency information.

Start by tracing how the current search reads catalog.json, since the issue notes that dependency information is not present there. Define where dependency data will come from and how it should be indexed; the work is done when users can find construct libraries by a dependency such as @aws-cdk/aws-ec2.

Written by the indexing model from the issue text.