Warn users if they are on an old IntelliJ plugin

If a user updates to the latest Flutter but is still using an old IntelliJ plugin we should warn them that they should also update their Flutter IntelliJ plugin to get the best experience.

Similarly, if a user hits an exception and is using an old IntelliJ plugin we should suggest they update their plugin to see if that fixes the issue before filing a bug.

This should help avoid bug reports like https://github.com/flutter/flutter-intellij/issues/3955 which cost our team time and lead users to think that our tools are buggy even when we have fixed the bugs.

The issue names no files or tests. Start by tracing how Flutter and IntelliJ plugin versions are exposed and where exceptions are surfaced; then determine how warnings should be shown for outdated plugins in both cases. Done means users receive an actionable update suggestion before filing a bug when the plugin is old.

Written by the indexing model from the issue text.