Validator is not detecting duplicate tags

[VisLab]

The HED validator is not correctly detecting duplicate tags that are extensions.

Example: Attribute/Red has no validation errors. Short-to-long conversion correctly detects the error:

Unable to convert HED string:
ERROR: 'Red' appears as 'Attribute/Sensory/Visual/Color/CSS-color/Red-color/Red' and cannot be used as an extension. 10, 13

Here is how I think this should be handled on validation.

1. No duplicate tags should ever allowed as extensions regardless of HED version. HED-2G and HED-3G both have Red in their hierarchy so Attribute/Red would always be an error regardless of HED version.
2. Tag extensions would always generate a warning, so Attribute/Bananas would always generate a warning regardless of the version since Bananas is a tag extension.

I think that putting in the restriction that tag extensions can't be in the hierarchy already simplifies the logic.
@IanCa @happy5214

[IanCa]

1. Should now be fixed with the new pull request.
2. Is not yet handled.

[IanCa]

This should be resolved as of a while ago.