Capture deprecation warnings in batched master tasks

[DaveCTurner]

It's possible for a cluster state update task to emit deprecation warnings, but if the task is executed in a batch then these warnings will be exposed to the listener for every item in the batch. With this commit we introduce a mechanism for tasks to capture just the warnings relevant to them, along with assertions that warnings are not inadvertently leaked back to the master service.

Closes #85506

[elasticmachine]

Pinging @elastic/es-distributed (Team:Distributed)

[DaveCTurner]

Not ready to merge, this needs testing in MasterServiceTests too, but before I start on that I want to see whether CI finds any other cases that need fixing and/or some more fundamental problems.

[elasticsearchmachine]

Hi @DaveCTurner, I've created a changelog YAML for you.

[DaveCTurner]

The Windows packaging test failure is definitely unrelated and I'm pretty sure the DiscoveryDisruptionIT is too - opened #86974 to track it.