Start on metal rendering infrastructure

gpui/src/platform/mac/shaders/shaders.h

@@ -0,0 +1,17 @@
+#include <simd/simd.h>
+
+typedef enum {
+    GPUIQuadInputIndexVertices = 0,
+    GPUIQuadInputIndexQuads = 1,
+    GPUIQuadInputIndexUniforms = 2,
+} GPUIQuadInputIndex;
+
+typedef struct {
+    vector_float2 origin;
+    vector_float2 size;
+    vector_float4 background_color;
+} GPUIQuad;
+
+typedef struct {
+    vector_float2 viewport_size;
+} GPUIQuadUniforms;