Clean up the 3D renderer for enhanced flexibility (#1895)

* Give `GPU2D::Unit` a virtual destructor

- Undefined behavior avoided!

* Add an `array2d` alias

* Move various parts of `GPU2D::SoftRenderer` to `constexpr`

- `SoftRenderer::MosaicTable` is now initialized at compile-time
- Most of the `SoftRenderer::Color*` functions are now `constexpr`
- The aforementioned functions are used with a constant value in at least one place, so they'll be at least partially computed at compile-time

* Generalize `GLRenderer::PrepareCaptureFrame`

- Declare it in the base `Renderer3D` class, but make it empty

* Remove unneeded `virtual` specifiers

* Store `Framebuffer`'s memory in `unique_ptr`s

- Reduce the risk of leaks this way

* Clean up how `GLCompositor` is initialized

- Return it as an `std::optional` instead of a `std::unique_ptr`
- Make `GLCompositor` movable
- Replace `GLCompositor`'s plain arrays with `std::array` to simplify moving

* Pass `GPU` to `GLCompositor`'s important functions instead of passing it to the constructor

* Move `GLCompositor` to be a field within `GLRenderer`

- Some methods were moved up and made `virtual`

* Fix some linker errors

* Set the renderer in the frontend

* Remove unneeded `virtual` specifiers

* Remove `RenderSettings` in favor of just exposing the relevant member variables

* Update the frontend to accommodate the core changes

* Add `constexpr` and `const` to places in the interpolator

* Qualify references to `size_t`

* Construct the `optional` directly instead of using `make_optional`

- It makes the Linux build choke
- I think it's because `GLCompositor`'s constructor is `private`

src/GPU3D_OpenGL.h

@@ -20,7 +20,7 @@
 
 #ifdef OGLRENDERER_ENABLED
 #include "GPU3D.h"
-
+#include "GPU_OpenGL.h"
 #include "OpenGLSupport.h"
 
 namespace melonDS
@@ -30,22 +30,31 @@ class GPU;
 class GLRenderer : public Renderer3D
 {
 public:
-    virtual ~GLRenderer() override;
-    virtual void Reset() override;
+    ~GLRenderer() override;
+    void Reset() override;
 
-    virtual void SetRenderSettings(const RenderSettings& settings) noexcept override;
+    void SetRenderSettings(bool betterpolygons, int scale) noexcept;
+    void SetBetterPolygons(bool betterpolygons) noexcept;
+    void SetScaleFactor(int scale) noexcept;
+    [[nodiscard]] bool GetBetterPolygons() const noexcept { return BetterPolygons; }
+    [[nodiscard]] int GetScaleFactor() const noexcept { return ScaleFactor; }
 
-    virtual void VCount144() override {};
-    virtual void RenderFrame() override;
-    virtual u32* GetLine(int line) override;
+    void VCount144() override {};
+    void RenderFrame() override;
+    void Stop() override;
+    u32* GetLine(int line) override;
 
     void SetupAccelFrame();
-    void PrepareCaptureFrame();
+    void PrepareCaptureFrame() override;
+    void Blit() override;
+
+    [[nodiscard]] const GLCompositor& GetCompositor() const noexcept { return CurGLCompositor; }
+    GLCompositor& GetCompositor() noexcept { return CurGLCompositor; }
 
     static std::unique_ptr<GLRenderer> New(melonDS::GPU& gpu) noexcept;
 private:
     // Used by New()
-    GLRenderer(melonDS::GPU& gpu) noexcept;
+    GLRenderer(GLCompositor&& compositor, GPU& gpu) noexcept;
 
     // GL version requirements
     // * texelFetch: 3.0 (GLSL 1.30)     (3.2/1.50 for MS)
@@ -66,6 +75,7 @@ private:
     };
 
     melonDS::GPU& GPU;
+    GLCompositor CurGLCompositor;
     RendererPolygon PolygonList[2048] {};
 
     bool BuildRenderShader(u32 flags, const char* vs, const char* fs);