Let hover suggest plugins

[GeertJohan]

Hover could suggest desktop-implementations of plugins.

1. For each dependency package in pubspec.yaml, detect if it's a plugin (uses platform-specific code).
2. For each plugin, see if it has a folder desktop with a go.mod file in it. If it has, assume it to be go-flutter compatible and suggest to the user to add it to desktop/cmd/options.go
3. For each plugin didn't satisfy point 2, see if there is a folder with the same name in go-flutter-desktop/plugins, then suggest adding that.

[GeertJohan]

Instead of 3, there may be a list.json file in the plugins repo linking plugins to desktop equivalents.

[GeertJohan]

Work has started in go-flutter-desktop/hover#7