Expose entire EndpointBuilder to filter factories

[halter73]

This flows the entire EndpointBuilder through to endpoint filter factories. This gives more context like the display name to filters, and reduces the number of properties in RequestDelegateFactoryOptions and EndpointFilterFactoryContext. And since the EndpointBuilder is usually a RouteEndpointBuilder, filters can observe the route pattern as well.

EndpointBuilder.RequestDelegate must be null if it is passed into the RequestDelegateFactory.Create(). The RequestDelegateFactory sets the RequestDelegate to the same instance returned via RequestDelegateResult.RequestDelegate. This is similar to how we were already mutating the passed-in metadata that was also then returned.

Fixes #43000

[halter73]

Closing in favor of #43543.