UncheckedIOException

### Affected version

HEAD

### Bug description

There are several UncheckedIOExceptions for issues that can definitely happen, and that are not handled where they should be. E.g.

```
protected Object eval(ScriptEngine engine, ScriptContext context) throws ScriptException {
try (FileReader reader = new FileReader(scriptFile)) {
return engine.eval(reader, context);
} catch (IOException ex) {
throw new UncheckedIOException(scriptFile + " caused:", ex);
}
}
```

This is risky and bug prone. Ideally these should be changed to IOException, but if API compatibility prevents that it looks like most could be replaced with a ScriptException instead.

Locate the ScriptEngine evaluation code containing the eval method and the FileReader/UncheckedIOException example, then review the other UncheckedIOException paths in the plugin. Check whether each case can expose IOException or must preserve API compatibility with ScriptException; done means the inappropriate unchecked exceptions are consistently replaced and the affected behavior is covered by the existing test suite.

Written by the indexing model from the issue text.