Intersection Over Union (IoU) should support Shape N x C_1 x C_2 x ... x C_n

[Shoumik-Gandre]

🐛 Bug

I was writing a Pull Request for Sorted AP metric and I figured "let's use torchmetrics's IOU function!". Unfortunately, unlike the JaccardIndex, torchmetric's IntersectionOverUnion does not take multiple dimensions.

Infact, it only allows the very limiting shape of (N, 4). This is not an oversight; it's a major flaw hurting torchmetric's credibility because IoU is the most well-known computer vision metric. A user will first look for IntersectionOverUnion and NOT JaccardIndex and chances are that they'll be disappointed.

I propose that IntersectionOverUnion be a wrapper over MultilabelJaccardIndex

I am willing to make a PR for it.

To Reproduce

See any example from here. IntersectionOverUnion