[azure-core] discrepancies between azure and unbranded pageable

[tadelesh]

in core, we have @pageItems to specify the the property that contains the array of page items. in azure core lib, we ahve @items to do the same thing. do we have plan to consolidate them?

[tadelesh]

also there are discrepancies for indicating if the operation is pageable. in azure, we use @pagedResult, in unbranded, we use @list. also, unbranded will check if there is at least @pageItems, but azure does not do validation for @items.

[lmazuel]

@markcowl I think the nextLink simplification was a good step, but we need more consolidation :)

[qiaozha]

I feel like we should also leverage the @list decorator in azure scope? using @pagedResult on a model to detect if it's a paging operation might be problematic if this model is being used in a non paging operation or being used as a property type of a non paging operation？