[video_core] Add SSAA antialiasing

Signed-off-by: lizzie <lizzie@eden-emu.dev>

src/video_core/host_shaders/ssaa.frag

@@ -0,0 +1,19 @@
+// SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#version 460
+#extension GL_ARB_sample_shading : enable
+
+#ifdef VULKAN
+#define BINDING_COLOR_TEXTURE 1
+#else // ^^^ Vulkan ^^^ // vvv OpenGL vvv
+#define BINDING_COLOR_TEXTURE 0
+#endif
+
+layout (location = 0) in vec4 posPos;
+layout (location = 0) out vec4 frag_color;
+layout (binding = BINDING_COLOR_TEXTURE) uniform sampler2D input_texture;
+
+void main() {
+  frag_color = texelFetch(input_texture, ivec2(posPos.xy * textureSize(input_texture)), gl_SampleID);
+}