Component id assignement is not consistent across PipelineContext instances

The "unique ref" ids used in PipelineContext are generated on the fly, which can cause us to get a different id for the same component in different contexts.

This becomes a problem when ExternalTransform is used, because it creates its own pipeline context for expansion. So its possible the component ids in the expansion request will actually refer to an entirely different component when the pipeline is finally assembled for execution.