examples: make sure some structs has guaranteed in-memory layout

examples/cubemap/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),

examples/ecs-app/physics2d.zig

@@ -16,7 +16,7 @@ pub const module = ecs.Module(.{
     .update = update,
 });
 
-pub const Vec2 = struct { x: f32, y: f32 };
+pub const Vec2 = extern struct { x: f32, y: f32 };
 
 fn update(msg: Message) void {
     switch (msg) {

examples/ecs-app/renderer.zig

@@ -10,4 +10,4 @@ pub const module = ecs.Module(.{
     // with renderer components like `.geometry` and render them for example!
 });
 
-pub const Vec3 = struct { x: f32, y: f32, z: f32 };
+pub const Vec3 = extern struct { x: f32, y: f32, z: f32 };

examples/fractal-cube/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),

examples/gkurve/atlas.zig

@@ -46,7 +46,7 @@ pub const Region = struct {
     }
 };
 
-pub const UVData = struct {
+pub const UVData = extern struct {
     bottom_left: @Vector(2, f32),
     width_and_height: @Vector(2, f32),
 };

examples/gkurve/draw.zig

@@ -7,7 +7,7 @@ const UVData = @import("atlas.zig").UVData;
 
 const Vec2 = @Vector(2, f32);
 
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     uv: Vec2,
 };
@@ -31,7 +31,7 @@ const GkurveType = enum(u32) {
     filled = 2,
 };
 
-pub const FragUniform = struct {
+pub const FragUniform = extern struct {
     type: GkurveType = .filled,
     // Padding for struct alignment to 16 bytes (minimum in WebGPU uniform).
     padding: @Vector(3, f32) = undefined,

examples/instanced-cube/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),

examples/pixel-post-process/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(3, f32),
     normal: @Vector(3, f32),
     uv: @Vector(2, f32),

examples/pixel-post-process/main.zig

@@ -16,7 +16,7 @@ const pixel_size = 8;
 const UniformBufferObject = struct {
     mat: zm.Mat,
 };
-const PostUniformBufferObject = struct {
+const PostUniformBufferObject = extern struct {
     width: u32,
     height: u32,
     pixel_size: u32 = pixel_size,

examples/pixel-post-process/quad_mesh.zig

@@ -1,4 +1,4 @@
-pub const Quad = struct {
+pub const Quad = extern struct {
     pos: @Vector(3, f32),
     uv: @Vector(2, f32),
 };

examples/rotating-cube/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),

examples/textured-cube/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),

examples/two-cubes/cube_mesh.zig

@@ -1,4 +1,4 @@
-pub const Vertex = struct {
+pub const Vertex = extern struct {
     pos: @Vector(4, f32),
     col: @Vector(4, f32),
     uv: @Vector(2, f32),