OptionsPlugins cannot be opened a second time after accepting or cancelling

To reproduce:
1. Open the OptionsLookAndFeel plugin (Edit >> Options >> Look and Feel...)
2. Press Cancel
3. Open the OptionsLookAndFeel plugin a second time
- Plugin does not open and IJ status bar shows message "Command cancelled: Look and Feel..."

This issue affects all plugins extending OptionsPlugin.

Start with OptionsLookAndFeel and the OptionsPlugin lifecycle, reproducing the cancel path and then opening the plugin again. Check both accepting and cancelling, including the shared behavior of plugins extending OptionsPlugin; done means every affected OptionsPlugin can be opened repeatedly without the cancellation status message.

Written by the indexing model from the issue text.