Bump protoc and gRPC versions for generated code

[tstirrat15]

Depends on https://github.com/grpc/grpc-java/issues/11015

Description

A customer noted a deprecation warning that they got when pulling in this library:

* @deprecated This class is deprecated, and slated for removal in the next Java breaking change
*     (5.x). Users should update gencode to >= 4.26.x which uses GeneratedMessage instead.
*/

@Deprecated
public abstract class GeneratedMessageV3
    extends GeneratedMessage.ExtendableMessage<GeneratedMessageV3> {

When I went and dug into it, we're currently on v25 of protobuf which corresponds to v3.25.x of the java protoc tooling. We want to be on v27, which is the currently-supported version.

There's more information in the support matrix here: https://protobuf.dev/support/version-support/#java

Note

There are breaking changes in the v26 release, which is a version boundary that we're crossing. It seems like most of the changes are related to features of the generated code that most consumers won't be using or aware of, but it may be prudent to make this a major version bump.

Changes

• Bump the version of the protoc plugin we're using
• Bump the gRPC version that we pull in

  Testing

  Review. See that things are green.

[tstirrat15]

The builds are still failing - it seems like there are some wires getting crossed around which version of protobuf-java is being used, but I can't figure out the right combination. Gonna come back to this.

[tstirrat15]

I think this is blocked behind the resolution of https://github.com/grpc/grpc-java/issues/11015#issuecomment-2315919862