renderer_base: Make creation of the rasterizer, the responsibility of the renderers themselves

Given we use a base-class type within the renderer for the rasterizer
(RasterizerInterface), we want to allow renderers to perform more
complex initialization if they need to do such a thing. This makes it
important to reserve type information.

Given the OpenGL renderer is quite simple settings-wise, this is just a
simple shuffling of the initialization code. For something like Vulkan
however this might involve doing something like:

// Initialize and call rasterizer-specific function that requires
// the full type of the instance created.
auto raster = std::make_unique<VulkanRasterizer>(some, params);
raster->CallSomeVulkanRasterizerSpecificFunction();

// Assign to base class variable
rasterizer = std::move(raster)

src/video_core/renderer_base.h

@@ -58,9 +58,6 @@ public:
     void RefreshBaseSettings();
 
 protected:
-    /// Refreshes settings specific to the rasterizer.
-    void RefreshRasterizerSetting();
-
     Core::Frontend::EmuWindow& render_window; ///< Reference to the render window handle.
     std::unique_ptr<RasterizerInterface> rasterizer;
     f32 m_current_fps = 0.0f; ///< Current framerate, should be set by the renderer