[core] add a `details` property on LROPoller

There are several services now (mostly cognitive, I believe) that expose long running operations which have relevant metadata on the operation. This metadata usually indicates the state of the operation one way or another. Here's an example in Text Analytics: https://github.com/Azure/azure-rest-api-specs/blob/main/specification/cognitiveservices/data-plane/Language/stable/2022-05-01/textanalytics.json#L2147

In order to expose this metadata on the poller, we have had to create custom poller implementations with the metadata as either read-only properties directly on the poller, or more preferably under a `details` property. If we moved this to the core implementation of LROPoller, we could make these custom implementations redundant.

The feature request is to add a `details` property to LROPoller/AsyncLROPoller in the shape of a `Mapping[str, Any]`. This way any service that supports operation-related info can populate the metadata dict and document simply as `LROPoller`.