Feature Request: add region testing to YAML

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Currently, only the block structure is part of the YAML representation, this means the Regions and their placement can not be tested effectively. As a numba developer I want to be able to test loop_restructure and branch_restructure effectively and for this I will need to be able to encode the expected result, including regions, in a simple YAML syntax.

Then -- once this syntax is established -- all the existing tests need to be refactored such that region testing is added to them.