Fix path/URL confusion in wxLaunchDefaultBrowser()

Add a helper wxLaunchBrowserParams struct with clearly distinct "url" and
"path" fields and GetPathOrURL() accessor which returns whichever is
appropriate.

This makes the code more clear and ensures that we never pass URLs (but only
file paths) to xdg-open under Unix as it doesn't handle them.

See #17227.

src/osx/utils_osx.cpp

@@ -36,6 +36,10 @@
 
 #include <AudioToolbox/AudioServices.h>
 
+#if wxUSE_GUI
+    #include "wx/private/launchbrowser.h"
+#endif
+
 #include "wx/osx/private.h"
 #include "wx/osx/private/timer.h"
 
@@ -130,11 +134,10 @@ bool wxLaunchDefaultApplication(const wxString& document, int flags)
 // Launch default browser
 // ----------------------------------------------------------------------------
 
-bool wxDoLaunchDefaultBrowser(const wxString& url, int flags)
+bool wxDoLaunchDefaultBrowser(const wxLaunchBrowserParams& params)
 {
-    wxUnusedVar(flags);
     wxCFRef< CFURLRef > curl( CFURLCreateWithString( kCFAllocatorDefault,
-                              wxCFStringRef( url ), NULL ) );
+                              wxCFStringRef( params.url ), NULL ) );
     OSStatus err = LSOpenCFURLRef( curl , NULL );
 
     if (err == noErr)