Importer test data.

Most files have a generation script except for when it is expected that they will never change. Things in that category and break glass instructions to update:

• LeakyReLU.onnx: Just a random single-op ONNX test to verify that the upstream importer is wired properly. It should never need to be updated but if it does, pretty much any single-op test case from the ONNX test suite will suffice.