PEL: Fixes for gcc13

* Add the cstdint header file as now required to get the uint* types.
* Fix a move assignment test
* Refactor some nlohmann::json code to avoid:

```
/usr/include/c++/13/valarray:1201:1: note:   template argument deduction/substitution failed:
../extensions/openpower-pels/registry.cpp:665:43: note:   ‘const nlohmann::json_abi_v3_11_2::basic_json<>::value_type’ {aka ‘const nlohmann::json_abi_v3_11_2::basic_json<>’} is not derived from ‘const std::valarray<_Tp>’
  665 |             (name == j["SRC"]["ReasonCode"] && type == LookupType::reasonCode));
```

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Ia3e733602134a60008d0d47934f95a217d2a0eb1
diff --git a/extensions/openpower-pels/user_data_json.hpp b/extensions/openpower-pels/user_data_json.hpp
index 9d6b79d..930e378 100644
--- a/extensions/openpower-pels/user_data_json.hpp
+++ b/extensions/openpower-pels/user_data_json.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cstdint>
 #include <optional>
 #include <string>
 #include <vector>