[data] add autocompletion to datapipes (#86960)
In REPLs (e.g. jupyter notebook) autocomplete now works:
<img width="750" alt="image" src="https://user-images.githubusercontent.com/53842584/195776448-f33180da-d1cd-4e47-b9a0-4fd9eb2f78b7.png">
even with custom data pipes:
<img width="804" alt="image" src="https://user-images.githubusercontent.com/53842584/195776957-5c51895e-f469-4b13-81ba-c9b507022555.png">
Unfortunately I wasn't able to figure out how to get autocomplete to work for non-REPLs (e.g. VSCode) - may need to generate fake pyi stubs, which 1) won't work for custom datapipes and 2) is a larger project to tackle :)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86960
Approved by: https://github.com/NivekT
