Update paging APIs to use updated SCM types

[annelo-msft]

In System.ClientModel 1.1.0-beta.5, PageableCollection<T> was changed to PageCollection<T> to better align convenience and protocol methods.

This PR upgrades the OpenAI library to SCM 1.1.0-beta.5, and manually implements internal types that will be generated from TypeSpec API specification in the future. Specifically, it:

• Updates return types that have been renamed for streaming service methods
• For service methods corresponding to paginated-collection endpoints
  • Returns PageCollection<T> or AsyncPageCollection<T> from convenience methods
  • Takes XxCollectionOptions types that describe the paginated collection to be returned
  • Adds "rehydration" methods that return a collection that starts where another collection type left off via a persisted rehydration token
  • Returns IEnumerable<ClientResult> or IAsyncEnumerable<ClientResult> from protocol methods, representing a collection of service responses, where each corresponds to a page of results returned from the paginated endpoint
  • Implements internal page enumerator and page token types for each paginated-endpoint operation

Types that are intended to be output by the generator have been added in a temporary folder called To.Be.Generated.