THRIFT-5817: [C++] Avoid copy of TUuid

[CJCombrink]

THRIFT-5817: [C++] Avoid copy of TUuid
Make TYPE_UUID as complex for C and C++ generator

• Generate code that does not make a copy for TUuid for C and C++

• Did you create an Apache Jira ticket? (Request account here, not required for trivial changes)
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
  This can be breaking, but not sure if it applies since I don't think UUID support has been released for C++
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.

[Jens-G]

Happy to merge into 0.21.0 but I want a second opinion here.

[jeking3]

The return value optimization to use a reference is probably a wash, since the value is going to sent through the protocol anyway. Maybe it provides a tiny memory savings.

Avoiding a copy on the input is a performance improvement and that's the one I thought would be useful.