Protobuf language support does not handle `oneof`

[ProPorygon]

The code highlighting support for text in protobuf format does not handle oneof fields. For example:

message OneofMessage {
    oneof choices {
        int32 some_number = 1;
        string some_string = 2;
    }
}

should be valid protobuf text, but code-blocks currently renders this as: with no highlighting and incorrect indentation.

[alexwforsythe]

Formatting seemed to work as expected when I tried to reproduce this:

Can you still reproduce this issue? If so, can you put the unformatted code in a public document and post a link to it in this issue?