Protobuf warnings in console

[alexander-yevsyukov]

The build of the mc-java-protoc contains the below warnings:

> Task :mc-java-protoc:test

`InterfaceGen` should > skip generation for types included in compilation but not requested to be generated STANDARD_ERROR
    Oct 05, 2022 7:32:48 PM com.google.protobuf.Descriptors$DescriptorPool lookupSymbol
    WARNING: The descriptor for message type ".spine.tools.protoc.msg.UserName" cannot be found and a placeholder is created for it

`InterfaceGen` should > not generate `UuidValue` insertion points for ineligible messages STANDARD_ERROR
    Oct 05, 2022 7:32:48 PM com.google.protobuf.Descriptors$DescriptorPool lookupSymbol
    WARNING: The descriptor for message type ".google.protobuf.Timestamp" cannot be found and a placeholder is created for it

Even though the root project applies ProtoData to all subprojects, descriptors does not seem to be generated under the build directory.

Applying buildSrc/.../ProtobufTaskExtensions.kt does not remove the warnings. Probably because desc.ref files are not added in the corresponding directories under the subproject.

The goal of this issue is to investigate the nature of warnings and address the cause.

[alexander-yevsyukov]

@armiol, FYI.