rasterizer_cache: Clear null surface to transparent

* Causes visual regressions in Pokemon with RADV

src/video_core/rasterizer_cache/rasterizer_cache.h

@@ -67,6 +67,16 @@ RasterizerCache<T>::RasterizerCache(Memory::MemorySystem& memory_,
                                            .wrap_s = TextureConfig::WrapMode::ClampToBorder,
                                            .wrap_t = TextureConfig::WrapMode::ClampToBorder,
                                        }));
+
+    auto& null_surface = slot_surfaces[NULL_SURFACE_ID];
+    runtime.ClearTexture(null_surface, {
+                                           .texture_level = 0,
+                                           .texture_rect = null_surface.GetScaledRect(),
+                                           .value =
+                                               {
+                                                   .color = {0.f, 0.f, 0.f, 0.f},
+                                               },
+                                       });
 }
 
 template <class T>

src/video_core/shader/generator/glsl_shader_gen.cpp

@@ -63,7 +63,13 @@ static std::string GetVertexInterfaceDeclaration(bool is_output, bool use_clip_p
     if (is_output && separable_shader) {
         // gl_PerVertex redeclaration is required for separate shader object
         out += "out gl_PerVertex {\n";
+        // Apple Silicon GPU drivers optimize more aggressively, which can create
+        // too much variance and cause visual artifacting in games like Pokemon.
+#ifdef __APPLE__
         out += "    invariant vec4 gl_Position;\n";
+#else
+        out += "    vec4 gl_Position;\n";
+#endif
         if (use_clip_planes) {
             out += "    float gl_ClipDistance[2];\n";
         }