Add x11 backend runner support (#22)

lib/commands/run.dart

@@ -13,14 +13,7 @@ import '../elinux_plugins.dart';
 
 class ELinuxRunCommand extends RunCommand with ELinuxExtension {
   ELinuxRunCommand({bool verboseHelp = false})
-      : super(verboseHelp: verboseHelp) {
-    argParser.addOption(
-      'target-backend-type',
-      defaultsTo: 'wayland',
-      allowed: <String>['wayland', 'gbm', 'eglstream', 'x11'],
-      help: 'Target backend type that the app will run on devices.',
-    );
-  }
+      : super(verboseHelp: verboseHelp);
 
   @override
   Future<Set<DevelopmentArtifact>> get requiredArtifacts async =>

lib/elinux_device_discovery.dart

@@ -121,7 +121,7 @@ class ELinuxDeviceDiscovery extends PollingDeviceDiscovery {
 
     // Adds current desktop host.
     devices.add(
-      ELinuxDevice('elinux',
+      ELinuxDevice('elinux-wayland',
           desktop: true,
           targetArch: _getCurrentHostPlatformArchName(),
           backendType: 'wayland',
@@ -134,6 +134,20 @@ class ELinuxDeviceDiscovery extends PollingDeviceDiscovery {
             processManager: const LocalProcessManager(),
           )),
     );
+    devices.add(
+      ELinuxDevice('elinux-x11',
+          desktop: true,
+          targetArch: _getCurrentHostPlatformArchName(),
+          backendType: 'x11',
+          logger: _logger ?? globals.logger,
+          processManager: _processManager ?? globals.processManager,
+          operatingSystemUtils: OperatingSystemUtils(
+            fileSystem: globals.fs,
+            logger: _logger ?? globals.logger,
+            platform: globals.platform,
+            processManager: const LocalProcessManager(),
+          )),
+    );
 
     // Adds remote devices.
     for (final ELinuxRemoteDeviceConfig remoteDevice