Improve ModuleBatchProcessor UI

[imagejan]

When there's only one batchable parameter, ModuleBatchProcessor displays a multi-file chooser dialog via uiService.chooseFiles().

The (IMHO much nicer) [Swing]FileListWidget is only shown (together with a choice dropdown) when there are multiple parameters that could be iterated in batch.

We should instead default to always display the widget, even if only a single "batchable" input is present. We could probably annotate inputFileList with (autofill=false), provided we accurately handle this annotation, see scijava/scijava-common#420.

batch-processor/src/main/java/org/scijava/batch/ModuleBatchProcessor.java

Lines 69 to 70 in e4e888c

	@Parameter(label = "Input files")
	private File[] inputFileList;

[imagejan]

/cc @tibuch