Desktop: Allow Electron debugging flag (#2084)

* Add check for Electron's cli arg --remote-debugging-port and discard it to prevent cli arg parser raising Unknown flag exception.

* Jump to next iteration once arg processed

* Allow only the strict form of flag as --x=y

ReactNativeClient/lib/BaseApplication.js

@@ -170,6 +170,12 @@ class BaseApplication {
 				continue;
 			}
 
+			if (arg.indexOf('--remote-debugging-port=') === 0) {
+				// Electron-specific flag used for debugging - ignore it. Electron expects this flag in '--x=y' form, a single string.
+				argv.splice(0, 1);
+				continue;
+			}
+
 			if (arg.length && arg[0] == '-') {
 				throw new JoplinError(_('Unknown flag: %s', arg), 'flagError');
 			} else {