gpu: add Surface.DescriptorFromMetalLayer

Signed-off-by: Stephen Gutekanst <stephen@hexops.com>

gpu/TODO-webgpu.h

@@ -1,8 +1,3 @@
-pub const WGPUSurfaceDescriptorFromMetalLayer = extern struct {
-    chain: ChainedStruct,
-    layer: *anyopaque,
-};
-
 pub const WGPUSurfaceDescriptorFromWaylandSurface = extern struct {
     chain: ChainedStruct,
     display: *anyopaque,

gpu/src/surface.zig

@@ -20,4 +20,9 @@ pub const Surface = enum(usize) {
         chain: ChainedStruct,
         selector: [*:0]const u8,
     };
+
+    pub const DescriptorFromMetalLayer = extern struct {
+        chain: ChainedStruct,
+        layer: *anyopaque,
+    };
 };