EXPERIMENTAL: Metal backend (#441)

This is not a continuation of the Metal backend; this is simply bringing
the branch up to date and merging it as-is behind an experiment.

---------

Co-authored-by: Isaac Marovitz <isaacryu@icloud.com>
Co-authored-by: Samuliak <samuliak77@gmail.com>
Co-authored-by: SamoZ256 <96914946+SamoZ256@users.noreply.github.com>
Co-authored-by: Isaac Marovitz <42140194+IsaacMarovitz@users.noreply.github.com>
Co-authored-by: riperiperi <rhy3756547@hotmail.com>
Co-authored-by: Gabriel A <gab.dark.100@gmail.com>

src/Ryujinx.Graphics.Metal/Shaders/BlitMs.metal

@@ -0,0 +1,45 @@
+#include <metal_stdlib>
+
+using namespace metal;
+
+struct CopyVertexOut {
+    float4 position [[position]];
+    float2 uv;
+};
+
+struct TexCoords {
+    float data[4];
+};
+
+struct ConstantBuffers {
+    constant TexCoords* tex_coord;
+};
+
+struct Textures
+{
+    texture2d_ms<FORMAT, access::read> texture;
+};
+
+vertex CopyVertexOut vertexMain(uint vid [[vertex_id]],
+                                constant ConstantBuffers &constant_buffers [[buffer(CONSTANT_BUFFERS_INDEX)]]) {
+    CopyVertexOut out;
+
+    int low = vid & 1;
+    int high = vid >> 1;
+    out.uv.x = constant_buffers.tex_coord->data[low];
+    out.uv.y = constant_buffers.tex_coord->data[2 + high];
+    out.position.x = (float(low) - 0.5f) * 2.0f;
+    out.position.y = (float(high) - 0.5f) * 2.0f;
+    out.position.z = 0.0f;
+    out.position.w = 1.0f;
+
+    return out;
+}
+
+fragment FORMAT4 fragmentMain(CopyVertexOut in [[stage_in]],
+                             constant Textures &textures [[buffer(TEXTURES_INDEX)]],
+                             uint sample_id [[sample_id]]) {
+    uint2 tex_size = uint2(textures.texture.get_width(), textures.texture.get_height());
+    uint2 tex_coord = uint2(in.uv * float2(tex_size));
+    return textures.texture.read(tex_coord, sample_id);
+}