We currently don't have any enforcement of the minimum sdk that we support (as defined in our supported platforms).

Despite increasing the minimum from 16 to 19, a fresh flutter app edited to have minSdkVersion 15 provides no error or warning. We should consider enforcing the minimum, or at least providing a warning.

We could also maybe use this to provide a warning 1 stable cut ahead of when we drop support for a version range, though I'm not sure that noise would be desirable.