Add flag to enable client method instrumentation

See https://github.com/Azure/azure-sdk-for-net/issues/55575. Initially attempted to do this as a visitor for the Azure on SCM libraries, but that doesn't really make sense since we can't reuse the Azure visitor. We should probably add first-class support for this and have it enabled by default. In the Azure emitter, we would turn off the instrumentation, but for libraries doing Azure on SCM it would be turned on.