SpecDB: Add OutTensor specs for add.Tensor & add.Scalar (#5)

Summary:
Pull Request resolved: #5

Added the out tensor spec for:
- add.Tensor: promoted type of inputs must be castable to out dtype
- add.Scalar: promoted type of inputs must be equal to out dtype

Prompted by Jarvis's adoption of FACTO-based testing on D59247125

Reviewed By: zonglinpengmeta

Differential Revision: D59402158

fbshipit-source-id: 784471e2b5494dbf82b5003c259ce75e9e63a323

Author: manuelcandales

specdb/db.py

@@ -341,7 +341,16 @@
             ),
         ],
         outspec=[
-            OutArg(ArgType.Tensor),
+            OutArg(
+                ArgType.Tensor,
+                constraints=[
+                    cp.Dtype.In(
+                        lambda deps: dt.can_cast_from(
+                            torch.promote_types(deps[0].dtype, deps[1].dtype)
+                        )
+                    ),
+                ],
+            ),
         ],
     ),
     Spec(
@@ -373,7 +382,16 @@
             ),
         ],
         outspec=[
-            OutArg(ArgType.Tensor),
+            OutArg(
+                ArgType.Tensor,
+                constraints=[
+                    cp.Dtype.Eq(
+                        lambda deps: (
+                            fn.promote_type_with_scalar(deps[0].dtype, deps[1])
+                        )
+                    ),
+                ],
+            )
         ],
     ),
     Spec(