Show unsupported platforms error message (#638)

This PR fixes fixes issue where error messages for unsupported platforms
were not displayed and prevents Xcode errors from appearing on Windows
by ensuring the checkXcodeExists function is only executed on macOS.

Previously, an error related to the OS const in `platform.ts` was always
thrown before the check in `extension.ts`. This change ensures the
verification process happens correctly.

Fixes #620 

### How Has This Been Tested: 
- run extension on currently unsupported platform (linux)
- run extension and check the logs for any errors caused by xcrun on
Windows


![image](https://github.com/user-attachments/assets/e509d0c1-ea0d-41da-bd01-3bee60c44989)

packages/vscode-extension/package.json

@@ -17,8 +17,7 @@
   ],
   "version": "0.0.20",
   "engines": {
-    "vscode": "^1.75.0",
-    "os": "darwin"
+    "vscode": "^1.75.0"
   },
   "extensionKind": [
     "workspace"

packages/vscode-extension/src/devices/DeviceManager.ts

@@ -108,7 +108,7 @@ export class DeviceManager implements DeviceManagerInterface {
 
     let shouldLoadSimulators = Platform.OS === "macos";
 
-    if (!(await checkXcodeExists())) {
+    if (shouldLoadSimulators && !(await checkXcodeExists())) {
       shouldLoadSimulators = false;
       Logger.debug("Couldn't list iOS simulators as XCode installation wasn't found");
     }

packages/vscode-extension/src/utilities/platform.ts

@@ -1,20 +1,21 @@
 import os from "os";
 
-const OS: "macos" | "windows" = (() => {
+const OS: "macos" | "windows" | "unsupported" = (() => {
   const platform = os.platform();
   switch (platform) {
     case "darwin":
       return "macos";
     case "win32":
       return "windows";
     default:
-      throw new Error("Unsupported platform");
+      return "unsupported";
   }
 })();
 export const Platform = {
   OS,
   select: <R, T>(obj: { macos: R; windows: T }) => {
-    return obj[Platform.OS];
+    // we assume that the 'unsupported' OS type will never occur here
+    return Platform.OS !== "unsupported" ? obj[Platform.OS] : obj["macos"];
   },
 };