Allow shadowing service fields when extending commands

[imagejan]

See fiji/FilamentDetector#24 (comment).

[imagejan]

Here's probably where we could change this, by excluding Service types from the check:

scijava-common/src/main/java/org/scijava/command/CommandInfo.java

Lines 462 to 468 in 46ca0d0

	final String name = f.getName();
	if (inputMap.containsKey(name) || outputMap.containsKey(name)) {
	// NB: Shadowed parameters are bad because they are ambiguous.
	final String error = "Invalid duplicate parameter: " + f;
	problems.add(new ValidityProblem(error));
	valid = false;
	}