Update on "[executorch][serialization] Rename scalar_type.fbs --> common.fbs"

Allow us to add other shared flatbuffer types into `common.fbs`.

- Rename scalar_type.fbs --> common.fbs
- Rename scalar_type.py --> common_schema.py (differentiate from exir/common.py)

Differential Revision: [D65442256](https://our.internmc.facebook.com/intern/diff/D65442256/)

[ghstack-poisoned]

Author: lucylq

exir/TARGETS

@@ -40,19 +40,20 @@ python_library(
     ],
 )
 
-# Deprecated in ExecuTorch v0.5
 python_library(
-    name = "scalar_type",
+    name = "common_schema",
     srcs = [
-        "scalar_type.py",
+        "common_schema.py",
     ],
 )
 
+# Deprecated in ExecuTorch v0.5
 python_library(
-    name = "common_schema",
+    name = "scalar_type",
     srcs = [
-        "common_schema.py",
+        "scalar_type.py",
     ],
+    deps = [":common_schema"],
 )
 
 python_library(