INT-3317: Remove `comparator` from `resequencer`

JIRA: https://jira.spring.io/browse/INT-3317

In addition add `AbstractCorrelatingMessageHandler.discardChannelName` for convenience with JavaConfig

INT-3317: Add `AbstractCorrMH.outputChannelName`

INT-3317: Fix further `BF` population

Also add `MessageFilter.discardChannelName`

Move `XPathExpressionEvaluatingHeaderValueMessageProcessor` to the `xml.transformer.support` package

Additional polishing

Polishing

PR comments.