Improve torch.ops typing (pytorch#11276)

Summary:

X-link: pytorch/pytorch#154555

Cloned pytorch/pytorch#153558 from benjaminglass1 and fixed internal typing errors.

Fixes longstanding issue where direct references to aten operations are seen as untyped by type checkers. This is accomplished by setting attributes on several classes more consistently, so that `__getattr__` can return a single type in all other cases.

Decisions made along the way:

1. `torch.ops.higher_order` is now implemented by a single-purpose class. This was effectively true before, but the class implementing it attempted to be generalized unnecessarily. Fixing this simplified typing for the `_Ops` class.
2. `__getattr__` is only called when all other lookup methods have failed, so several constant special-cases in the function could be implemented as class variables.

The remainder of this PR is fixing up all the bugs exposed by the updated typing, as well as all the nitpicky typing issues.

Reviewed By: bobrenjc93

Differential Revision: D75497142

Author: aorenste

backends/cadence/aot/quantizer/patterns.py

@@ -109,6 +109,7 @@ def get_anchors(
         )
 
     def replacement_op(self) -> OpOverload:
+        # pyre-ignore: Incompatible return type [7]: Expected `OpOverload` but got `OpOverloadPacket`.
         return torch.ops.cadence.quantized_linear