Add tests for StableHLO Models

[ScottTodd]

See also

• Add tests for StableHLO operators #4
• Add tests for ONNX models  #6
• Add tests for TFLite models #5
• Add tests for PyTorch models #63

This new "stablehlo-exports" repository could also be useful: https://github.com/GleasonK/stablehlo-exports, at least for testing that compilation succeeds. The weights are elided in some programs though.