LUCENE-10046: Fix counting bug in StringValueFacetCounts

[gsmiller]

Description

Fixes a counting bug in StringValueFacetCounts exposed on a specific execution path.

Solution

Make sure to map to a global ordinal as necessary.

Tests

Added a new test case to expose the issue.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Lucene maintainers access to contribute to my PR branch. (optional but recommended)
• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.

[gsmiller]

Pushing this fix without a review since as it's a simple change and kind of a nasty edge-case bug. Happy to iterate on this / incorporate feedback post-push if anyone has thought though.