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`

1 files changed, 3 insertions, 2 deletions

diff --git a/src/Wifi.h b/src/Wifi.h
index c47a883..76fa146 100644
--- a/src/Wifi.h
+++ b/src/Wifi.h
@@ -24,7 +24,7 @@
 namespace melonDS
 {
 class WifiAP;
-
+class NDS;
 class Wifi
 {
 public:
@@ -157,7 +157,7 @@ public:
         W_RXTXAddr = 0x268,
     };
 
-    Wifi();
+    Wifi(melonDS::NDS& nds);
     ~Wifi();
     void Reset();
     void DoSavestate(Savestate* file);
@@ -173,6 +173,7 @@ public:
     u8* GetBSSID();
 
 private:
+    melonDS::NDS& NDS;
     u8 RAM[0x2000];
     u16 IO[0x1000>>1];