Stabilize `UseCompressor` and `SetSendCompressor` about grpc-go HOT 1 OPEN

Anything documented as "deprecated" but that doesn't also state that it may/will be removed in the future, will be supported throughout 1.x releases, so WithCompressor can be used without worrying that it will be broken. (Newer deprecation notices explicitly state something like "Will be supported throughout 1.x.") "Deprecated" in this sense means "there are better ways of doing the same thing", either performance-wise or ergonomically or both.

For reference, our full versioning policy is here: https://github.com/grpc/grpc-go/blob/master/Documentation/versioning.md

Because the UseCompressor feature is still marked as experimental, there may be future changes we want to make to the API, so it would be better to avoid it if you aren't willing to update your code if we do make changes there.

In order to stabilize UseCompressor, we would really like to receive feedback from our users that the API works well for them. We haven't had any complaints, but we don't really know who is using this feature, either. We are considering some changes to the encoding package (that contains the compressor and codec interfaces), but that would affect the implementers of codecs/compressors, not uses of them. So it may be the case that we could stabilize UseCompressor and SetSendCompressor without needing to stabilize the encoding package.

from grpc-go.