Fix warning with torch.meshgrid

[pallgeuer]

Motivation

torch.meshgrid() has started raising a warning when not called with an explicit indexing parameter:
https://pytorch.org/docs/stable/generated/torch.meshgrid.html

Modification

Provide indexing='ij' to all calls to torch.meshgrid that don't already specify indexing.

[pallgeuer]

Refer to open-mmlab/mmdetection#8090 (comment) for discussion on PyTorch version support of torch.meshgrid.

[GT9505]

Very appreciate your contribution.

After discussing a general solution in your posted pr of mmdet, we can use the same behavior to fix the bug.

[pallgeuer]

I have updated the PR based on the same solution used for mmpose and mmdet.

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