Move outplace ops to ATen (#16788)

Summary:
Based on https://github.com/pytorch/pytorch/pull/12413, with the following additional changes:

-  Inside `native_functions.yml` move those outplace operators right next to everyone's corresponding inplace operators for convenience of checking if they match when reviewing
- `matches_jit_signature: True` for them
- Add missing `scatter` with Scalar source
- Add missing `masked_fill` and `index_fill` with Tensor source.
- Add missing test for `scatter` with Scalar source
- Add missing test for `masked_fill` and `index_fill` with Tensor source by checking the gradient w.r.t source
- Add missing docs to `tensor.rst`

Differential Revision: D14069925

Pulled By: ezyang

fbshipit-source-id: bb3f0cb51cf6b756788dc4955667fead6e8796e5

torch/_tensor_docs.py

@@ -2963,6 +2963,55 @@ pinverse() -> Tensor
 See :func:`torch.pinverse`
 """)
 
+add_docstr_all('index_add',
+               r"""
+index_add(dim, index, tensor) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.index_add_`
+""")
+
+add_docstr_all('index_copy',
+               r"""
+index_copy(dim, index, tensor) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.index_copy_`
+""")
+
+add_docstr_all('index_fill',
+               r"""
+index_fill(dim, index, value) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.index_fill_`
+""")
+
+add_docstr_all('scatter',
+               r"""
+scatter(dim, index, source) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.scatter_`
+""")
+
+add_docstr_all('scatter_add',
+               r"""
+scatter_add(dim, index, source) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.scatter_add_`
+""")
+
+add_docstr_all('masked_scatter',
+               r"""
+masked_scatter(mask, tensor) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.masked_scatter_`
+""")
+
+add_docstr_all('masked_fill',
+               r"""
+masked_fill(mask, value) -> Tensor
+
+Out-of-place version of :meth:`torch.Tensor.masked_fill_`
+""")
+
 add_docstr_all('grad',
                r"""
 This attribute is ``None`` by default and becomes a Tensor the first time a call to