Rework iree_tests configs to list passing tests as well as failing tests?

[ScottTodd]

Config files (mostly used for the ONNX test suite) use this schema: https://github.com/nod-ai/SHARK-TestSuite/blob/16812962da23c85302c03ef505f4c654cb54b46c/iree_tests/conftest.py#L25-L52

(aside: that schema could be encoded in a file for validation/reference, rather than just included in a comment)

Right now test cases are included in one of these lists or not mentioned at all

• skip_compile_tests
• skip_run_tests
• expected_compile_failures
• expected_run_failures

While this lets us add new tests without needing to update existing files, it doesn't make it clear how many tests are included and which are passing.

Now that test results can be automatically reflected back into config files using https://github.com/nod-ai/SHARK-TestSuite/blob/main/iree_tests/update_config_xfails.py, we could for example

A) also list passing tests:

"passing_tests": [
  "test_abs",
]

B) list test statuses directly:

"tests": {
  "test_abs": "pass",
  "test_add": "skip_compile",
  "test_div": "skip_run",
  "test_mul": "fail_compile",
  "test_sub": "fail_run",
}