StreamsMetricsImpl contains several convenience methods for safely registering sensors at different levels of granularity. We added them as internal methods because we weren't sure of their stability and utility. Now, they've been in use for quite a while and seem to be stable.
We should move them up into the public API so that custom stores and processor implementations can also benefit from their safety.
Implementing this feature should also allow us to drop the adaptor function: `org.apache.kafka.streams.processor.internals.ProcessorContextUtils#getMetricsImpl`
Note: this feature requires a KIP, but since the API is already pre-determined, it should be uncontroversial. This improvement would be a good opportunity for someone who wants to get an initial KIP under their belt.