Rewrite the macOS renderer using CAMetalLayer

This allows v-sync to be disabled on macOS and lets us remove a whole bunch of old hacks.

Further optimizations of the new renderer are still needed.

app/shaders/vt_renderer.metal

@@ -0,0 +1,35 @@
+using namespace metal;
+
+struct Vertex
+{
+    float4 position [[ position ]];
+    float2 texCoords;
+};
+
+struct CscParams
+{
+    float3 matrix[3];
+    float3 offsets;
+};
+
+constexpr sampler s(coord::normalized, address::clamp_to_edge, filter::linear);
+
+vertex Vertex vs_draw(constant Vertex *vertices [[ buffer(0) ]], uint id [[ vertex_id ]])
+{
+    return vertices[id];
+}
+
+fragment float4 ps_draw_biplanar(Vertex v [[ stage_in ]],
+                                 constant CscParams &cscParams [[ buffer(0) ]],
+                                 texture2d<float> luminancePlane [[ texture(0) ]],
+                                 texture2d<float> chrominancePlane [[ texture(1) ]])
+{
+    float3 yuv = float3(luminancePlane.sample(s, v.texCoords).r, chrominancePlane.sample(s, v.texCoords).rg);
+    yuv -= cscParams.offsets;
+
+    float3 rgb;
+    rgb.r = dot(yuv, cscParams.matrix[0]);
+    rgb.g = dot(yuv, cscParams.matrix[1]);
+    rgb.b = dot(yuv, cscParams.matrix[2]);
+    return float4(rgb, 1.0f);
+}