add official qml extension to devcontainer.json

.devcontainer/devcontainer.json

@@ -19,6 +19,7 @@
 				"samuelcolvin.jinjahtml",
 				"seanwu.vscode-qt-for-python",
 				"sourcery.sourcery",
+				"theqtcompany.qt-qml",
 				"zxh404.vscode-proto3"
 			]
 		}