[MetaSchedule] Enable Task Filtering

[junrushao]

This PR allows relay.backend.MetaScheduleExtractTask to take an extra argument filter_func which filters out tasks that don't need tuning. The counterpart of AutoScheduler is traverse_to_get_io_tensors.

[junrushao]

CC: @comaniac @Hzfengsy @zxybazh

[Hzfengsy]

Can we add testcases?

[comaniac]

Overall LGTM. Echo @Hzfengsy's comment that we may need a test case.

[junrushao]

@Hzfengsy thanks for asking! It's pretty hard to add a unittest given we will need an actual end-to-end network that takes hours to run...In this particular case, it might be good to leave it to future integration test instead

[comaniac]

IIUC, unit tests for task extraction don't need to run tune. Instead, it only needs to extract tasks and verify their number and workloads. However, if MetaSchedule doesn't have unit tests for task extractions yet, we could of course add it later.

[junrushao]

I'm happy to add a simple unittest without tuning :-)