warn user when Android SDK in IDEA doesn't match "flutter doctor"

To reproduce:
- create a new Flutter project
- on the "android" module, see that the Module SDK is "Android API 25 Platform"
- create the Android SDK to match, setting this to a different android home than the one reported by "flutter doctor"

We don't warn about this, but it could easily happen accidentally, resulting in confused users. We should show a warning somewhere if the Android SDK is different.

The issue provides a reproduction using a Flutter project’s android module and the Android SDK reported by "flutter doctor," but names no files or tests. Start by tracing where the plugin reads the module SDK and Flutter’s Android SDK path; done means showing a warning when those SDKs differ.

Written by the indexing model from the issue text.