add platform message and response

Author: quoid

extension/Userscripts Extension/SafariWebExtensionHandler.swift

@@ -17,7 +17,15 @@ class SafariWebExtensionHandler: NSObject, NSExtensionRequestHandling {
         // these if/else if statement are formatted so that they can be neatly collapsed in Xcode
         // typically the "else if" would be on the same line as the preceding statements close backet
         // ie. } else if {
-        if name == "REQ_USERSCRIPTS" {
+        if name == "REQ_PLATFORM" {
+            var platform:String
+            #if os(iOS)
+                platform = "ios"
+            #elseif os(macOS)
+                platform = "macos"
+            #endif
+            response.userInfo = [SFExtensionMessageKey: ["platform": platform]]
+        } else if name == "REQ_USERSCRIPTS" {
             if let url = message?["url"] as? String, let isTop = message?["isTop"] as? Bool {
                 if
                     checkDefaultDirectories(),