[qute] @CheckedTemplate(requireTypeSafeExpressions = false) is ignored

With a checked template defined as

    @CheckedTemplate(requireTypeSafeExpressions = false)
    public static class Templates {
        public static native TemplateInstance item(Item item); 
    }

The validation still complains about {toto} can't be resolved as a variable.

I'm not too sure how to handle requireTypeSafeExpressions here since it's a warning already, that's still valuable information.

If we make the diagnostic severity configurable, i.e. severity.UndefinedVariable=error, would we have to automatically downgrade it to warning if we detect requireTypeSafeExpressions = false?

@maxandersen @mkouba you got an opinion?

Start by tracing checked-template validation for @CheckedTemplate and the UndefinedVariable diagnostic. Determine how requireTypeSafeExpressions = false should affect that diagnostic, then verify that the resulting severity or behavior matches the intended configuration without suppressing valuable information.