Update `get_*_features` methods + update doc snippets (#40555)
* siglip
* clip
* aimv2
* metaclip_2
* align
* align fixup
* altclip
* blip2 (make consistent)
* chineese clip
* clipseg
* flava
* groupvit
* owlv2
* owlvit
* vision_encoder
* clap
* x_clip
* fixup
* fix siglip2
* blip2
* fix blip2 tests (revert to original)
* fix docs