[RTG][Elaboration] Support sequences

[maerhart]

• Simplify materializer to work on only one basic block
• Remove unused addWorklist argument and use a class field instead
• Because the way invocations are elaborated has changed, we don't need the worklist anymore within sequences or tests (we can just iterate over the operations since it's not a graph region), this is a big performance benefit in large tests/sequences.
• Do a BFS over the sequence invocation hierarchy such that callees are only elaborated when all parents are elaborated (because only the sequence_closure operation should fix the randomization within a sequence, thus they create a clone before elaborating the referenced sequence)
• Inline all sequences and remove them.