Demo indexing custom ordinal data in the taxonomy

### Description

#12337 introduced the possibility of indexing data about facet labels directly into the taxonomy.
We should write a [facets demo](https://github.com/apache/lucene/tree/main/lucene/demo/src/java/org/apache/lucene/demo/facet) for this functionality and mention it in the [faceting guide](https://github.com/apache/lucene/blob/main/lucene/demo/src/java/org/apache/lucene/demo/facet/package-info.java). The unit tests in the PR can be a starting point.

Start with the unit tests from PR #12337, then inspect the existing examples in lucene/demo/src/java/org/apache/lucene/demo/facet. Add a facets demo for indexing custom ordinal data into the taxonomy and mention it in lucene/demo/src/java/org/apache/lucene/demo/facet/package-info.java; done means the demo and guide cover this functionality.

Written by the indexing model from the issue text.