Various cleanups to ir_emitter and friends (#46686)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46686
I was trying to page this code back in after a while and some things
stuck out as unnecessarily confusing.
1. Improve documentation of closures and fork stuff to be more accurate
to how we use them today.
2. Change `prim::LocalVariableScope` to `prim::ListComprehension`. It is
only ever used for a list comprehensions, and in general the nodes
emitted by `ir_emitter` should correspond to concrete operations or
language features rather than semantic constraints.
3. Change the somewhat mysterious "inputs" and "attributes" argument
names throughout the codebase to be the more obvious "args" and "kwargs"
that they generally represent (I think "inputs" and "attributes" come
from the AST naming).
Test Plan: Imported from OSS
Reviewed By: navahgar, jamesr66a
Differential Revision: D24464197
Pulled By: suo
fbshipit-source-id: 1f4b1475b58b5690a0b204e705caceff969533b4
