InstCountCI: Support encoding expected Arm64 ASM in JSON

This will allow investigating the Arm64 directly next to the test, plus
publicly linking directly to badly behaving tests.

Perfect for nerdsniping implementations.

Scripts/UpdateInstructionCountJson.py

@@ -13,7 +13,11 @@ def update_performance_numbers(performance_json_path, performance_json, new_json
         if not key in performance_json["Instructions"]:
             logging.error("{} didn't exist in performance json file?".format(key))
             return 1
-        performance_json["Instructions"][key]["ExpectedInstructionCount"] = items
+
+        if "ExpectedInstructionCount" in items:
+            performance_json["Instructions"][key]["ExpectedInstructionCount"] = items["ExpectedInstructionCount"]
+        if "ExpectedArm64ASM" in items:
+            performance_json["Instructions"][key]["ExpectedArm64ASM"] = items["ExpectedArm64ASM"]
 
     # Output to the original file.
     with open(performance_json_path, "w") as json_file: