Split OpenCensus Shim between Trace/metrics

[jsuereth]

Is your feature request related to a problem? Please describe. Tracing is going GA prior to Metrics. We should split the OpenCensus shim so that the tracing portion can go stable with the OpenTelemetry Tracing and allow metrics to evolve with metrics.

Describe the solution you'd like Split the opencenus shim into two components.

Describe alternatives you've considered Delaying OpenCensus shim until post metrics GA

[hdost]

did this split already happen? or is this necessary at this point?

[jkwatson]

I don't think we have a spec for exactly how all of this is supposed to work yet.