CBG-4430: fix conflict on hlv comparison when parent rev is in history

[gregns1]

CBG-4430

• Create a shared function to test for rev tree conflicts
• On failed conflict check in between hlv's we should check for rev tree conflict when we have rev tree history to work with
• If we don't check rev tree history conflict on hlv comparison then we still need to after hlv comparisons

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/000/