Mask R-CNN with MobileNet v3 backbone

[niladridutt]

🚀 Feature

Add Mask R-CNN with MobileNet v3 backbone

Motivation

In the recent release torchvision added support for mobilenet v3 and extended it to work with instance segmentation models.
torchvision.models.detection.fasterrcnn_mobilenet_v3_large_fpn
However, support for Mask R-CNN with MobileNet v3 backbone is still missing and would be a worthy addition.

Pitch

• Similar module like torchvision.models.detection.fasterrcnn_mobilenet_v3_large_fpn but to work with Mask R-CNN like resnet has torchvision.models.detection.maskrcnn_resnet50_fpn
• MobileNet V3 would make inference much faster
• Mask R-CNN is widely used owing to its dual use of getting mask+bounding box

[datumbox]

@niladridutt Thanks, makes sense. We can have a look at it.

[niladridutt]

Thanks!

[oke-aditya]

Let's add this to #2707 as well :)