Currently plugin_tools tries to drive every example app unconditionally for iOS and Android. This means that a *_macos, *_linux, etc. federated plugin package needs to have example/ios/* and example/android/* even though it doesn't implement them, or tests will (pointlessly) fail. See flutter/plugins#2589 for an example.

We should make the tooling check the (local, not app-facing) plugin's supported platforms for mobile as we do for desktop. We'll need to either retool the is-platform-x-supported check to understand the legacy plugin: section in pubspec.yaml, or ensure that all plugins in flutter/plugins are using the new schema (the latter may already be done, I'm not sure offhand if it was done comprehensively).