Integer overflow in total count in grouping results [LUCENE-9302]

When doing a Grouping search in solr cloud you can get a negative number for the total found.

This is caused by the accumulated total being held in an integer and not a long.

example result:

` "responseHeader": { "status": 0, "QTime": 9231, "params": { "q": "decade:200", "indent": "true", "fl": "decade", "wt": "json", "group.field": "decade", "group": "true", "_": "1542773674247" } }, "grouped": { "decade": { "matches": -629516788, "groups": [ { "groupValue": "200", "doclist": { "numFound": -629516788, "start": 0, "maxScore": 1.9315376, "docs": [ { "decade": "200" } ] } } ] } } `}

`result without grouping:`
` "responseHeader": { "status": 0, "QTime": 1063, "params": { "q": "decade:200", "indent": "true", "fl": "decade", "wt": "json", "_": "1542773791855" } }, "response": { "numFound": 3665450508, "start": 0, "maxScore": 1.9315376, "docs": [ { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" }, { "decade": "200" } ] } `}

---
Migrated from [LUCENE-9302](https://issues.apache.org/jira/browse/LUCENE-9302) by Ian, 1 vote, updated Apr 06 2020
Attachments: [SOLR-13004.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-9302/SOLR-13004.patch) (versions: 2)
Linked issues:
- [SOLR-14381](https://issues.apache.org/jira/browse/SOLR-14381)

Start by reviewing the attached SOLR-13004.patch and locating the grouping-search implementation responsible for accumulated totals. Reproduce the reported grouped versus ungrouped count discrepancy; done when grouped totals remain correct beyond the integer range, with appropriate regression coverage.

Written by the indexing model from the issue text.