Consider sharing code for warning about ignoring CIF/SVG declarations
Many CIF tools have something like:
```java
// Remove/ignore I/O declarations, to increase the supported subset.
RemoveIoDecls removeIoDecls = new RemoveIoDecls();
removeIoDecls.transform(spec);
if (removeIoDecls.haveAnySvgInputDeclarationsBeenRemoved()) {
warnOutput.line("The specification contains CIF/SVG input declarations. These will be ignored.");
}
```
The warning should be consistent. We may want to move that to the transformation, or to some common plugin, or so.
issue