Refactor NDS and DSi to be objects (#1893)

* First crack at refactoring NDS and DSi into objects

- Remove all global/`static` variables in `NDS` and related classes
- Rely more on virtual dispatch when we need to pick methods at runtime
- Pass `NDS&` or `DSi&` to its constituent components where necessary
- Introduce some headers or move some definitions to break `#include` cycles

* Refactor the frontend to accommodate the core's changes

* Move up `SchedList`'s declaration

- Move it to before the components are initialized so the `map`s inside are initialized
- Fields in C++ are initialized in the order they're declared

* Fix a crash when allocating memory

* Fix JIT-free builds

* Fix GDB-free builds

* Fix Linux builds

- Explicitly qualify some member types in NDS, since they share the same name as their classes

* Remove an unnecessary template argument

- This was causing the build to fail on macOS

* Fix ARM and Android builds

* Rename `Constants.h` to `MemConstants.h`

* Add `NDS::IsRunning()`

* Use an `#include` guard instead of `#pragma once`

src/AREngine.h

@@ -23,12 +23,11 @@
 
 namespace melonDS
 {
+class NDS;
 class AREngine
 {
 public:
-    AREngine();
-    ~AREngine();
-    void Reset();
+    AREngine(melonDS::NDS& nds);
 
     ARCodeFile* GetCodeFile() { return CodeFile; }
     void SetCodeFile(ARCodeFile* file) { CodeFile = file; }
@@ -36,15 +35,8 @@ public:
     void RunCheats();
     void RunCheat(ARCode& arcode);
 private:
+    melonDS::NDS& NDS;
     ARCodeFile* CodeFile; // AR code file - frontend is responsible for managing this
-
-    // TEMPORARY
-    u8 (*BusRead8)(u32 addr);
-    u16 (*BusRead16)(u32 addr);
-    u32 (*BusRead32)(u32 addr);
-    void (*BusWrite8)(u32 addr, u8 val);
-    void (*BusWrite16)(u32 addr, u16 val);
-    void (*BusWrite32)(u32 addr, u32 val);
 };
 
 }