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/DMA.h

@@ -21,17 +21,16 @@
 
 #include <array>
 #include "types.h"
-#include "Savestate.h"
-#include "DMA_Timings.h"
 
 namespace melonDS
 {
-class GPU;
+class NDS;
+class Savestate;
 
 class DMA
 {
 public:
-    DMA(u32 cpu, u32 num, GPU& gpu);
+    DMA(u32 cpu, u32 num, NDS& nds);
     ~DMA() = default;
 
     void Reset();
@@ -46,12 +45,8 @@ public:
     u32 UnitTimings7_16(bool burststart);
     u32 UnitTimings7_32(bool burststart);
 
-    template <int ConsoleType>
     void Run();
-
-    template <int ConsoleType>
     void Run9();
-    template <int ConsoleType>
     void Run7();
 
     bool IsInMode(u32 mode) const noexcept
@@ -83,7 +78,7 @@ public:
     u32 Cnt {};
 
 private:
-    melonDS::GPU& GPU;
+    melonDS::NDS& NDS;
     u32 CPU {};
     u32 Num {};