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/DSi_SPI_TSC.cpp

@@ -28,7 +28,7 @@ using Platform::Log;
 using Platform::LogLevel;
 
 
-DSi_TSC::DSi_TSC(SPIHost* host) : TSC(host)
+DSi_TSC::DSi_TSC(melonDS::DSi& dsi) : TSC(dsi)
 {
 }
 
@@ -198,7 +198,7 @@ void DSi_TSC::Write(u8 val)
                     {
                         Log(LogLevel::Debug, "DSi_SPI_TSC: DS-compatibility mode\n");
                         DataPos = 0;
-                        NDS::KeyInput |= (1 << (16+6));
+                        NDS.KeyInput |= (1 << (16+6));
                         return;
                     }
                 }