Add IBaseRequestBuilder interface to BaseRequestBuilder class

[michael-hawker]

This seems to be the only implementation of a RequestBuilder which doesn't have its corresponding interface?

This is part of a problem (also see https://github.com/microsoftgraph/msgraph-sdk-dotnet/issues/722) for anything use BaseFunctionMethodRequestBuilder as a RequestBuilder because it doesn't implement the interface and inherits from the base class directly here:

msgraph-sdk-dotnet-core/src/Microsoft.Graph.Core/Requests/BaseFunctionMethodRequestBuilder.cs

Line 13 in 61405c1

public abstract class BaseFunctionMethodRequestBuilder<T> : BaseRequestBuilder where T : IBaseRequest

Therefore things like the IDriveRecentRequestBuilder's implementation is not compatible to case to a generic IBaseRequestBuilder:

https://github.com/microsoftgraph/msgraph-sdk-dotnet/blob/9b74c2674969008669e4c46ac85bda7e6ad8a728/src/Microsoft.Graph/Requests/Generated/DriveRecentRequestBuilder.cs#L19

public partial class DriveRecentRequestBuilder : BaseFunctionMethodRequestBuilder<IDriveRecentRequest>, IDriveRecentRequestBuilder

This prevents a nice common way to receive RequestBuilders for general calls to the graph and make them on behalf of a developer as part of an auxiliary API.

[michael-hawker]

FYI it looks like your pipeline is trying to run in my user context or something and failing based on permissions? (That's outside the scope of this fix, but seems like something that should be investigated)

[michael-hawker]

@MIchaelMainer @darrelmiller any status on this?