Abstract Backend testing logic

[skywall]

🚀 The feature, motivation and pitch

Backend testing lacks reusable base Tester class. To improve extensibility, let's refactor XNNPACKTester into a more abstract BackendTester and move it to backends/test. XNNPACKTester, ArmTester, and a new NeutronTester should then derive from BackendTester.

Alternatives

No response

Additional context

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RFC (Optional)

No response

cc @digantdesai @mcr229 @cbilgin @cccclai

[mcr229]

yea we've been meaning to do something like this. The idea would be that the Tester Base class stays the same, but each backend will have their own configurable stages (Export, Quantize, ToBackend, etc..) And backends can configure those stages to do what their expected flow is (for example XNNPACK's ToBackend stage would choose XNNPACKPartitioner to lower the model). I believe @GregoryComer has some other ideas for auto generating tests as well to give all backends native strong coverage.

[GregoryComer]

Yeah, having common delegate test infra would be helpful across the board. Ideally we can use it to make common backend tests "plug and play" with each delegate by dropping in the relevant tester implementation.