ECPoint compressed state and 1.64

When trying to migrate from BC 1.63 to 1.64, which was advertised as a
security release, I noticed compressed state has been removed from ECPoint.

I see two problems:

- If I'm not mistaken, this breaking change hasn't been documented in
the release notes.
- Putting breaking changes into a security release is detrimental to
quick rollout of the respective security fixes.

I understand that we should only use compressed pubkeys. However in
reality lots of uncompressed pubkeys are out in the wild and we still
need to interoperate with them. In the case of Bitcoin, they're frozen
into the blockchain. What's the recommended migration path for apps that
still need to deal with uncompressed keys?