Consider implementing this as an analyzer plugin

[evanweible-wf]

Currently, we detect dependency usages with regex matching. This is fast, but can produce false positives (#21). It's also separate tool that needs to be run manually and added to CI.

To address these, we should consider implementing the current logic as a plugin to the Dart analysis server. Users would get results as a part of their existing static analysis (including via IDEs for more immediate and continuous feedback).