Add more TS lints (#6084)

* Fix to not call onMouseLeave with no selected object

* Add no this alias lint

* Add more lints and fix JSON formatting

* Fix to use lower-case string type

* Add another namespace lint

* Fix to not use plus on possibly non-string values

src/lang/std/engineConnection.ts

@@ -591,6 +591,7 @@ class EngineConnection extends EventTarget {
    * did not establish.
    */
   connect(reconnecting?: boolean): Promise<void> {
+    // eslint-disable-next-line @typescript-eslint/no-this-alias
     const that = this
     return new Promise((resolve) => {
       if (this.isConnecting() || this.isReady()) {