raco: enable serializing temp relations to Myria backend

Before merging to Myria-web, will require uwescience/myria#tbd
On the Myria side, a `DoWhile` is a body and the name of a relation to scan to get the loop condition.

On the Raco side, when compiling to `myrialang` we force the termination condition to be a `StoreTemp` wrapping the singleton boolean expression that is the terminal condition. (That already happens as of when we merged DoWhile support in.)