Add facemesh support

[chmjkb]

Model: https://github.com/tiqq111/mediapipe_pytorch

[chmjkb]

This issue is blocked by the following issue in upstream: pytorch/executorch#18663. I tried cherry-picking that fix and rebuilding the runtime, however the issue was still there. Setting this to blocked until this gets resolved.

[JakeStevens]

@chmjkb can you provide a minimal reproducible for the errors you see as well? The PR seems to cover it, I have re-created it here:

pytorch/executorch#21480

As the original PR is abandoned. I've added a regression test for the const buffer and load from file usecases. Can you help clarify what the remaining bug is?

Thanks!