Add Tensor.scatter_reduce (#8947)

* pytorch scatter -> scatter_reduce

* WIP scatter_reduce implementation

* _pre_scatter return type hint

* split out src, mask to satisfy linter

* Add src cast back in

* dict of lambdas instead of ifs

* sum and prod reduction ops with include_self

* add reduce arg error message

* add amax and amin reduction ops

* Fix include_self for higher dims

* Simplify

* Simplify amax and amin too

* Pull include_self logic out into _inv_mask function

* reduce arg cannot be None for scatter_reduce

* Fix self-mask issue

* Add mean reduce op

* Add tests

* any() not needed here

* remove comment

* End support for Tensor src with reduce arg in tinygrad scatter

* Process index, dim inside actual functions

* Add scatter_reduce to onnx

* Add excluded onnx ScatterElements reduction tests back in

* Save 2 lines on the mask helpers

* Update docs

* Add include_self=False tests

* cleanup

* Remove unneeded helper function

---------

Co-authored-by: chenyu <chenyu@fastmail.com>

docs/tensor/ops.md

@@ -32,6 +32,7 @@
 ::: tinygrad.Tensor.tril
 ::: tinygrad.Tensor.interpolate
 ::: tinygrad.Tensor.scatter
+::: tinygrad.Tensor.scatter_reduce
 
 ## Neural Network (functional)