Add WidgetStyle utility class to centralize style logic

[imagejan]

This pull request addresses #333 and is a first step toward fixing #197 and #382.

The methods in the new WidgetStyle utility class should replace isStyle() implementations and other case logic around (possibly multiple) style attributes of parameters in the following places:

• scijava-ui-swing:

  • chooseFile and chooseFiles in AbstractSwingUI
  • createFileFilter in SwingFileWidget
  • some helper methods in SwingChoiceRadioWidget

• batch-processor:

  • getTargetWidgetStyle in FileBatchInputProvider

• imagej-plugins-batch:

  • getTargetWidgetStyle in DatasetBatchInputProvider

• here in imagej-legacy, and finally

• some places in scijava-ui-awt, and three times in scijava-ui-pivot

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Remaining questions:

• I wasn't sure about the naming of getStyleModifiers. The intended use case is for styles like "extensions:tiff/tif" to get the list of allowed extensions, but there might be more general use cases.

• Should getStyleModifiers return an array of strings directly from split("/")? Or rather a Set<String> with trimmed, lower-case values?

[imagejan]

Thanks @ctrueden for merging this.
In the light of scijava/scijava-ui-swing#52, I now think we should maybe replace/modify getStyleModifiers to do something a bit more general, i.e. return everything after the : (String instead of String[]) and leave it to the caller to split the returned string (e.g. in the case of multiple extensions, such as extensions:tiff/tif) or to use the returned string entirely (e.g. with format:#0.000).

Now that 2.85.0 is released, we probably have to keep the API for backwards compatibility, right? : )

[ctrueden]

Now that 2.85.0 is released, we probably have to keep the API for backwards compatibility, right? : )

If we change it immediately, I'd be OK with breaking it. It's not part of pom-scijava et al. yet.