Add `fx-gltf` package (#494)

* Add fx-gltf package

* Update xmake.lua

packages/f/fx-gltf/xmake.lua

@@ -0,0 +1,25 @@
+package("fx-gltf")
+
+    set_kind("library", {headeronly = true})
+    set_homepage("https://github.com/jessey-git/fx-gltf")
+    set_description("A C++14/C++17 header-only library for simple, efficient, and robust serialization/deserialization of glTF 2.0")
+    set_license("MIT")
+
+    add_urls("https://github.com/jessey-git/fx-gltf/archive/refs/tags/$(version).tar.gz")
+    add_urls("https://github.com/jessey-git/fx-gltf.git")
+
+    add_versions("v1.2.0", "d8eaceba72ea6574b982c7b0d2328fd3f8ad519db4a37cf63cd3f8020d7722bf")
+
+    add_deps("nlohmann_json")
+
+    on_install(function(pkg)
+        os.cp("include/fx/gltf.h", pkg:installdir("include", "fx"))
+    end)
+
+    on_test(function(pkg)
+        assert(pkg:check_cxxsnippets({test = [[
+            void test() {
+                fx::gltf::Document doc;
+            }
+        ]]}, {configs = {languages = {"c++14", "c++17"}}, includes = "fx/gltf.h"}))
+    end)