Add background removal pipeline

[xenova]

This PR makes it far easier to use background-removal models.

import { pipeline } from '@huggingface/transformers';

const segmenter = await pipeline('background-removal', 'onnx-community/BEN2-ONNX');
const url = 'https://huggingface.co/datasets/Xenova/transformers.js-docs/resolve/main/woman-with-afro_medium.jpg';
const output = await segmenter(url);
output[0].save('mask.png');

Input	Output

Tested with:

• ✅ https://huggingface.co/Xenova/modnet
• ✅ https://huggingface.co/briaai/RMBG-1.4
• ✅ https://huggingface.co/briaai/RMBG-2.0
• ✅ https://huggingface.co/onnx-community/mediapipe_selfie_segmentation
• ✅ https://huggingface.co/onnx-community/mediapipe_selfie_segmentation_landscape
• ✅ https://huggingface.co/onnx-community/modnet-webnn
• ✅ https://huggingface.co/onnx-community/BiRefNet-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet_lite-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet-portrait-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet-COD-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet-DIS5K-TR_TEs-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet-DIS5K-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet-HRSOD_DHU-ONNX
• ✅ https://huggingface.co/onnx-community/BiRefNet_512x512-ONNX
• ✅ https://huggingface.co/onnx-community/ormbg-ONNX
• ✅ https://huggingface.co/onnx-community/BEN2-ONNX
• ✅ https://huggingface.co/onnx-community/MVANet-ONNX
• ✅ https://huggingface.co/onnx-community/ISNet-ONNX

TODO:

• Update model cards

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[JonasDoesThings]

Thanks so much for the work @xenova!

Could you maybe share your testing code that worked for briaai/RMBG-2.0? Trying to get it to work myself, but creating the pipeline fails with a strange numeric error and the PR only contains tests for 2 other models 😅