feat: add support for mach-glfw using Zig v2024.1.0-mach

src/gui.zig

@@ -7,7 +7,7 @@
 pub const plot = @import("plot.zig");
 pub const backend = switch (@import("zgui_options").backend) {
     .glfw_wgpu => @import("backend_glfw_wgpu.zig"),
-    .glfw_opengl3 => @import("backend_glfw_opengl.zig"),
+    .glfw_opengl3, .mach_glfw_opengl3 => @import("backend_glfw_opengl.zig"),
     .glfw_dx12 => @import("backend_glfw_dx12.zig"),
     .win32_dx12 => .{}, // TODO:
     .no_backend => .{},