Add accumulate to index_put_

[BalashovK]

Issue 758 is closed.
It says:
it you need the 'accumulate' argument on index_put, please open a new issue specifically calling for that.

I need "accumulate" in index_put_

My use-case: list of 2D indices with duplicates, which need to be rasterized over 2D canvas, summing up the duplicates.
I needed it for 2 projects already (physics & microbiology).
So far I have being using a trick with sparse-dense tensor conversion (for some reason, it adds values during the conversion instead of overriding them), but that is an undocumented feature and a questionable long-term solution.

Thank you!

[NiklasGustafsson]

This has not been forgotten. I'm onboarding additional engineering resources at Microsoft, and I'm going to use fixing this bug as a part of that process.