Refactor ipmi::sensor::GetSensorResponse away from std::array

This change refactors GetSensorResponse from std::array to struct.
This change depends on change #23544.

GetSensorResponse is an internal, intermediate structure, an unpacked
form of a Get Sensor Reading response, providing direct access to its
fields. Its life time is:
GetReadingResponse -> GetSensorResponse -> ipmi::RspType.

It is written to in 5 functions in the ipmi::sensor::get namespace, by
four setter functions (setOffset, setReading, setAssertionBytes,
enableScanning).
It is currently read from by 1 function (ipmiSensorGetSensorReading)
for transforming to an ipmi::RspType.

Originally, the setter functions assumed bitwise equivalence between
GetSensorResponse and GetReadingResponse, and the setter functions
used reinterpret_cast to assign to a GetSensorResponse as if it were
a GetReadingResponse.

With this change, the reinterpret_cast's are removed, and the set
functions now accept GetSensorResponse instead of GetReadingResponse,
so the code gets a bit easier to read.

Tested: Tested using a server with a BMC; sensor readings obtained
through `ipmitool` appear to be correct (the reading might change
within a small range):
 # ipmitool raw 0x04 0x2d 0x16
   9B 40 00 00

Signed-off-by: Sui Chen <suichen@google.com>
Change-Id: I5d454d6249f5431fb98169e6ef7c585c34024004
diff --git a/sensordatahandler.hpp b/sensordatahandler.hpp
index 129cbb4..99c3ae9 100644
--- a/sensordatahandler.hpp
+++ b/sensordatahandler.hpp
@@ -156,7 +156,6 @@
 {
     sdbusplus::bus::bus bus{ipmid_get_sd_bus_connection()};
     GetSensorResponse response{};
-    auto responseData = reinterpret_cast<GetReadingResponse*>(response.data());
 
     auto service = ipmi::getService(bus, sensorInfo.sensorInterface,
                                     sensorInfo.sensorPath);
@@ -166,8 +165,7 @@
         sensorInfo.propertyInterfaces.begin()->first,
         sensorInfo.propertyInterfaces.begin()->second.begin()->first);
 
-    setAssertionBytes(static_cast<uint16_t>(std::get<T>(propValue)),
-                      responseData);
+    setAssertionBytes(static_cast<uint16_t>(std::get<T>(propValue)), &response);
 
     return response;
 }
@@ -184,10 +182,10 @@
 GetSensorResponse readingData(const Info& sensorInfo)
 {
     sdbusplus::bus::bus bus{ipmid_get_sd_bus_connection()};
-    GetSensorResponse response{};
-    auto responseData = reinterpret_cast<GetReadingResponse*>(response.data());
 
-    enableScanning(responseData);
+    GetSensorResponse response{};
+
+    enableScanning(&response);
 
     auto service = ipmi::getService(bus, sensorInfo.sensorInterface,
                                     sensorInfo.sensorPath);
@@ -228,8 +226,7 @@
 
     auto rawData = static_cast<uint8_t>((value - sensorInfo.scaledOffset) /
                                         sensorInfo.coefficientM);
-
-    setReading(rawData, responseData);
+    setReading(rawData, &response);
 
     return response;
 }