Add shape documentation for CosineEmbeddingLoss (#58403)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/52732
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58403
Reviewed By: HDCharles
Differential Revision: D28480076
Pulled By: jbschlosser
fbshipit-source-id: c2c51e9da86e274e80126bbcabebb27270f2d2d0
