Prepare CLI for move into mainline

packages/cli/src/plugin/interface/os.rs

@@ -0,0 +1,18 @@
+use mlua::UserData;
+
+pub struct PluginOS;
+impl UserData for PluginOS {
+    fn add_methods<'lua, M: mlua::UserDataMethods<'lua, Self>>(methods: &mut M) {
+        methods.add_function("current_platform", |_, ()| {
+            if cfg!(target_os = "windows") {
+                Ok("windows")
+            } else if cfg!(target_os = "macos") {
+                Ok("macos")
+            } else if cfg!(target_os = "linux") {
+                Ok("linux")
+            } else {
+                panic!("unsupported platformm");
+            }
+        });
+    }
+}