Register grid_priors nn.Module test (#4489)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4489

Register customized op `grid_priors` in nn.Module test. Now it can be exported from PyTorch nn.module to Vulkan.

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Reviewed By: jorgep31415

Differential Revision: D60474638

fbshipit-source-id: 0ae75300f5833d9b0fb0565e639500b4b507b4b4