chore: convert extension apis to TypeScript (#18688)

Converts extensions-related files to TS

lib/renderer/extensions/event.ts

@@ -0,0 +1,20 @@
+export class Event {
+  private listeners: Function[] = []
+
+  addListener (callback: Function) {
+    this.listeners.push(callback)
+  }
+
+  removeListener (callback: Function) {
+    const index = this.listeners.indexOf(callback)
+    if (index !== -1) {
+      this.listeners.splice(index, 1)
+    }
+  }
+
+  emit (...args: any[]) {
+    for (const listener of this.listeners) {
+      listener(...args)
+    }
+  }
+}