add header only package mscharconv (#2566)

* add header only package mscharconv

* simplify code snippet

* simplify again

packages/m/mscharconv/xmake.lua

@@ -0,0 +1,26 @@
+package("mscharconv")
+    set_kind("library", {headeronly = true})
+    set_homepage("https://github.com/iboB/mscharconv")
+    set_description("<charconv> from Microsoft STL, but multi-platform ")
+
+    add_urls("https://github.com/iboB/mscharconv.git")
+    add_versions("latest", "5d2e3a6e9663a41207561c9510ad1e3d557b5c5e")
+
+    on_install(function (package)
+        os.cp("include", package:installdir())
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            void test(){
+                double pi = 3.14159265359;
+                char pi_str[256];
+                auto [p, ec] = msstl::to_chars(pi_str, pi_str + sizeof(pi_str), pi);
+            }
+            void test2(){
+                std::string_view pi_str = "3.14159 is pi";
+                double pi;
+                auto [p, ec] = msstl::from_chars(pi_str.data(), pi_str.data() + pi_str.length(), pi);
+            }
+        ]]}, {configs = {languages = "cxx17"}, includes = {"msstl/charconv.hpp", "iostream", "string_view"}}))
+    end)