POM: bump to scijava-common 2.21.1

This is for the WidgetModel.isModel(String) method.
SwingTextWidget: use isStyle(String) method

This ensures that if a widget has multiple associated styles, the tests
still work.
SwingNumberWidget: use isStyle(String) method

This ensures that if a widget has multiple associated styles, the tests
still work.
SwingChoiceRadioWidget: use isStyle(String) method

This ensures that if a widget has multiple associated styles, the tests
still work.
SwingTextWidget: use isStyle(String) method

This ensures that if a widget has multiple associated styles, the tests
still work.

This change also calls the UIService's chooseFile method instead of
hardcoding use of the JFileChooser here.
Merge branch 'widget-style'

This branch makes the Swing widgets use the WidgetModel#isStyle method
when checking style. This is more robust than using a string equality
test, because we want to support the possibility of multiple
comma-separated widget styles.