Test MV3 model in CI wheel builds (#9192)

### Summary

As part of https://github.com/pytorch/executorch/issues/9019, we want to
ensure we can export models on P0 hosts targeting P0 backends. So, let's
test this in our wheel creation. For now, we introduce macOS/Linux
XNNPACK export.

Given the wheel building GitHub workflow doesn't support using jobs as a
test step, we must go use a python script. This runs a similar test to
what we do in PRs:


https://github.com/pytorch/executorch/blob/1011fdc98bcd61063b845670fb1779635aa30e3a/.github/workflows/pull.yml#L85-L136

### Test plan

CI → Build {Linux, macOS} Wheels

cc @larryliu0820 @lucylq