Implement in-memory savestates (#1693)

* Refactor Savestate::Var{8,16,32,64}

- They now delegate to VarArray
- They're declared in the class header so they're likely to be inlined

* First crack at refactoring Savestate to work in-memory

- Well, third, but who's counting?

* Implement Savestate::Finish

* Remove the VersionMajor and VersionMinor fields

- Instead, pull their values directly from the savestate buffer

* Mark a new constructor as explicit

* Rename Reset to Rewind

* Fix a linebreak

* Implement Savestate::Rewind

* Add ROMManager::ClearBackupState

* Refactor ROMManager to use the refactored Savestate

* Capitalize "Least"

- It was driving me nuts

* Add a log call

* Increase default Savestate buffer length to 32MB

* Use C-style file I/O instead of C++-style

- Dumping bytes to a file with C++'s standard library is a MONSTROUS PAIN IN THE ASS

* Quote the savestate's file path for clarity

* Write the savestate's length into the header

* Add some extra logging calls

* Fix section-loading

* Remove the deprecated Savestate constructor

* Convert a char* to a u32 with memcpy, not a cast

* Fix section-handling in loads

* Include <cstring> in Savestate.h

- This was causing a build error on Linux

src/NDS.cpp

@@ -815,7 +815,10 @@ bool DoSavestate(Savestate* file)
         u32 console;
         file->Var32(&console);
         if (console != ConsoleType)
+        {
+            Log(LogLevel::Error, "savestate: Expected console type %d, got console type %d. cannot load.\n", ConsoleType, console);
             return false;
+        }
     }
 
     file->VarArray(MainRAM, MainRAMMaxSize);
@@ -870,7 +873,11 @@ bool DoSavestate(Savestate* file)
 
     file->VarArray(DMA9Fill, 4*sizeof(u32));
 
-    if (!DoSavestate_Scheduler(file)) return false;
+    if (!DoSavestate_Scheduler(file))
+    {
+        Platform::Log(Platform::LogLevel::Error, "savestate: failed to %s scheduler state\n", file->Saving ? "save" : "load");
+        return false;
+    }
     file->Var32(&SchedListMask);
     file->Var64(&ARM9Timestamp);
     file->Var64(&ARM9Target);
@@ -937,6 +944,8 @@ bool DoSavestate(Savestate* file)
     }
 #endif
 
+    file->Finish();
+
     return true;
 }