[Tests] Replace the Relay interpreter with the VM in the op tests

[gigiblender]

This PR disables, if possible, the Relay interpreter in the op level tests and enables the VM instead. It also parameterizes some of the tests to switch easily between the interpreter and other executors when further support is provided.

@areusch

[areusch]

@mbs-octoml @altanh can you take a look?

[mbs-octoml]

Thanks.

In case you're wondering, the weird idiom in these tests where the create_executor / evaluate / apply phases are all brought together is because the create_executor phase supports including an IRModule who's definitions should be 'visible' to the evaluate expression. However in practice all that happens is the IRModule and expression to be evaluated are joined together and compiled as a unit. Thus we should probably collapse the create_executor and evaluate phases, and the code was reworked to make that job easier in the future.

[gigiblender]

Thanks for the explanation @mbs-octoml.

I can see that for some reason even though you approved the changes, the PR wasn't merged automatically.

[masahi]

@gigiblender Approving and merging need separate actions (anyone can approve, but only a committer can merge).

[gigiblender]

Thanks for the clarification @masahi.