Add JSON vs. XML deserialization benchmark (Azure#3196)

Author: heaths

sdk/core/azure_core/Cargo.toml

@@ -96,6 +96,11 @@ features = [
 name = "benchmarks"
 harness = false
 
+[[bench]]
+name = "deserialization"
+harness = false
+required-features = ["xml"]
+
 [[bench]]
 name = "http_transport_benchmarks"
 harness = false