video_core: Eliminate the g_renderer global variable

We move the initialization of the renderer to the core class, while
keeping the creation of it and any other specifics in video_core. This
way we can ensure that the renderer is initialized and doesn't give
unfettered access to the renderer. This also makes dependencies on types
more explicit.

For example, the GPU class doesn't need to depend on the
existence of a renderer, it only needs to care about whether or not it
has a rasterizer, but since it was accessing the global variable, it was
also making the renderer a part of its dependency chain. By adjusting
the interface, we can get rid of this dependency.

src/core/core.h

@@ -27,6 +27,10 @@ namespace Service::SM {
 class ServiceManager;
 }
 
+namespace VideoCore {
+class RendererBase;
+}
+
 namespace Core {
 
 class System {
@@ -127,11 +131,26 @@ public:
     /// Gets a CPU interface to the CPU core with the specified index
     Cpu& CpuCore(size_t core_index);
 
-    /// Gets the GPU interface
+    /// Gets a mutable reference to the GPU interface
     Tegra::GPU& GPU() {
         return *gpu_core;
     }
 
+    /// Gets an immutable reference to the GPU interface.
+    const Tegra::GPU& GPU() const {
+        return *gpu_core;
+    }
+
+    /// Gets a mutable reference to the renderer.
+    VideoCore::RendererBase& Renderer() {
+        return *renderer;
+    }
+
+    /// Gets an immutable reference to the renderer.
+    const VideoCore::RendererBase& Renderer() const {
+        return *renderer;
+    }
+
     /// Gets the scheduler for the CPU core that is currently running
     Kernel::Scheduler& CurrentScheduler() {
         return *CurrentCpuCore().Scheduler();
@@ -195,6 +214,7 @@ private:
 
     /// AppLoader used to load the current executing application
     std::unique_ptr<Loader::AppLoader> app_loader;
+    std::unique_ptr<VideoCore::RendererBase> renderer;
     std::unique_ptr<Tegra::GPU> gpu_core;
     std::shared_ptr<Tegra::DebugContext> debug_context;
     Kernel::SharedPtr<Kernel::Process> current_process;