Fix opening URLS with special characters in macOS

The Online Tutorials section of InputMap in the editor's built-in
documentation viewer contains this link:

docs.godotengine.org/en/latest/tutorials/inputs/inputevent.html#inputmap

The macOS implementation for opening a link percent-encodes it before
sending it to the browser, resulting in a 404. This is to fix #13422
where filenames with special characters could not be opened in Finder.
However, this breaks URLS so I added a check to see if the resource
scheme is file:// and if so, only then is it escaped. This allows other
schemes like `http`, `ftp`, and `mailto` to be used.

platform/osx/os_osx.mm

@@ -272,7 +272,13 @@ String OS_OSX::get_system_dir(SystemDir p_dir) const {
 }
 
 Error OS_OSX::shell_open(String p_uri) {
-	[[NSWorkspace sharedWorkspace] openURL:[[NSURL alloc] initWithString:[[NSString stringWithUTF8String:p_uri.utf8().get_data()] stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLFragmentAllowedCharacterSet]]]];
+	NSString *string = [NSString stringWithUTF8String:p_uri.utf8().get_data()];
+	NSURL *uri = [[NSURL alloc] initWithString:string];
+	// Escape special characters in filenames
+	if (!uri || !uri.scheme || [uri.scheme isEqual:@"file"]) {
+		uri = [[NSURL alloc] initWithString:[string stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLFragmentAllowedCharacterSet]]];
+	}
+	[[NSWorkspace sharedWorkspace] openURL:uri];
 	return OK;
 }