MemArena: Name shared memory handle

Assign a name to the CreateFileMapping handle on Win32 so third party
applications can read from Dolphin's memory and integrate with the
current emulation.

Built and tested, multiple sessions are still possible without
collisions.

Source/Core/Common/MemArena.cpp

@@ -55,8 +55,8 @@ static int AshmemCreateFileMapping(const char* name, size_t size)
 void MemArena::GrabSHMSegment(size_t size)
 {
 #ifdef _WIN32
-  hMemoryMapping =
-      CreateFileMapping(INVALID_HANDLE_VALUE, nullptr, PAGE_READWRITE, 0, (DWORD)(size), nullptr);
+  hMemoryMapping = CreateFileMapping(INVALID_HANDLE_VALUE, nullptr, PAGE_READWRITE, 0,
+                                     static_cast<DWORD>(size), L"Dolphin-emu");
 #elif defined(ANDROID)
   fd = AshmemCreateFileMapping("Dolphin-emu", size);
   if (fd < 0)