Fix position embeddings singular/plural (#33678)
* fix position embeddings
* [run-slow] blip, blip_2, instructblip, instructblipvideo
* fix init
* [run-slow] blip, blip_2, instructblip, instructblipvideo
* fix copies
* [run-slow] blip, blip_2, instructblip, instructblipvideo
* [run-slow] blip, blip_2, instructblip, instructblipvideo
* handle exception where list + tensors are cat'd
* [run-slow] blip, blip_2, instructblip, instructblipvideo
* add missing default
* [run-slow] blip, blip_2, instructblip, instructblipvideo