wx: Add WX_MACOS_NON_GUI_APP

We cannot depend on `is_packaged_app()` check because it is not a
perfect way of checking if app is bundled.

It would return true when the app is bundled with a launcher like this:

```swift
import AppKit

let task = Process()
task.launchPath = "/Users/wojtek/src/otp/bin/erl"
task.arguments = ["-noshell", "-eval", "wx:new(), timer:sleep(5000), halt()"]
try task.run()
task.waitUntilExit()
```

It would return false for this launcher, however:

```swift
import AppKit

class AppDelegate: NSObject, NSApplicationDelegate {
    func applicationDidFinishLaunching(_ aNotification: Notification) {
        let task = Process()
        task.launchPath = "/Users/wojtek/src/otp/bin/erl"
        task.arguments = ["-noshell", "-eval", "wx:new(), timer:sleep(5000), halt()"]
        try! task.run()
    }
}

let app = NSApplication.shared
let delegate = AppDelegate()
app.delegate = delegate
app.run()
```

Btw, there has recently been a fix in wx [1] and we'd only be
able to take advantage of it when `OSXIsGUIApplication` returns true
(and when wx recognizes our app as properly bundled, see [2]).
And so I believe to support variety of scenarios, we need precise
control.

[1] https://github.com/wxWidgets/wxWidgets #22508
[2] https://github.com/erlang/otp #6070

lib/wx/c_src/wxe_impl.cpp

@@ -225,14 +225,16 @@ void WxeApp::MacReopenApp() {
   send_msg("reopen_app", &empty);
 }
 
+// See: https://github.com/wxWidgets/wxWidgets/blob/v3.1.5/src/osx/cocoa/utils.mm#L76:L93
 bool WxeApp::OSXIsGUIApplication() {
-  // wx manually activates the application if it's not in the bundle [1]. In particular, it calls
-  // `[NSApp setActivationPolicy: NSApplicationActivationPolicyRegular]` which prevents the app
-  // from running in the background and we cannot control it with `LSUIElement` [2]. Their check
-  // if it's a bundle always returns false for wxErlang. Thus we use our own way of detecting it.
-  // [1] https://github.com/wxWidgets/wxWidgets/blob/v3.1.5/src/osx/cocoa/utils.mm#L76:L93
-  // [2] https://developer.apple.com/documentation/bundleresources/information_property_list/lsuielement
-  return !is_packaged_app();
+   char val_buf[8];
+   size_t val_len = 7;
+   int res = enif_getenv("WX_MACOS_NON_GUI_APP", val_buf, &val_len);
+   if (res == 0) {
+     return FALSE;
+   } else {
+     return TRUE;
+   }
 }
 #endif