Common/Random: Add convenience template for simple arithmetic values

In cases where we just want a random value for a primitive arithmetic
type, we can wrap this in a template to allow convenient direct
assignment instead of keeping declaration and initialization separate
(making it more difficult to use values uninitialized). This also allows
the use of Common::Random with functions such as std::generate, making
it more flexible in how random values can be generated.

Source/Core/Common/TraversalServer.cpp

@@ -169,8 +169,7 @@ static sockaddr_in6 MakeSinAddr(const TraversalInetAddress& addr)
 static void GetRandomHostId(TraversalHostId* hostId)
 {
   char buf[9];
-  u32 num;
-  Common::Random::Generate(&num, sizeof(num));
+  const u32 num = Common::Random::GenerateValue<u32>();
   sprintf(buf, "%08x", num);
   memcpy(hostId->data(), buf, 8);
 }