[ADD] runtime/utils: optional validation to EventBus

Currently the event bus allows sending and listening to arbitrary
events, I got got by that when I pushed a fix using `addEventListener`
on a bus across an events renaming, and on the other side the fix did
nothing anymore. Entirely my fault, but if the list of events sent on
a bus is known and documented (e.g. a jsdoc has `@emits` tags) it
would make sense for both the listening and the dispatching to also be
validated.

This proposal performs validation only when the eventbus is created:

- in dev mode (which also requires being in a component context)
- if an iterable of events is passed to the ctor

The dev-mode check might be overkill but it seems like a good idea at
least for an initial version, as the validation does have a cost
however low, and validation errors can occur essentially anywhere.

src/runtime/utils.ts

@@ -1,4 +1,5 @@
 import { OwlError } from "../common/owl_error";
+import { ComponentNode, getCurrent } from "./component_node";
 export type Callback = () => void;
 
 /**
@@ -81,10 +82,52 @@ export function validateTarget(target: HTMLElement | ShadowRoot) {
 }
 
 export class EventBus extends EventTarget {
+  constructor(events?: string[]) {
+    if (events) {
+      let node: ComponentNode | null = null;
+      try {
+        node = getCurrent();
+      } catch {}
+      if (node?.app?.dev) {
+        return new DebugEventBus(events);
+      }
+    }
+    super();
+  }
   trigger(name: string, payload?: any) {
     this.dispatchEvent(new CustomEvent(name, { detail: payload }));
   }
 }
+class DebugEventBus extends EventBus {
+  private events: Set<string>;
+  constructor(events: string[]) {
+    super();
+    this.events = new Set(events);
+  }
+  addEventListener(
+    type: string,
+    listener: EventListenerOrEventListenerObject | null,
+    options?: boolean | AddEventListenerOptions
+  ): void {
+    if (!this.events.has(type)) {
+      throw new OwlError(`EventBus: subscribing to unknown event '${type}'`);
+    }
+    super.addEventListener(type, listener, options);
+  }
+  trigger(name: string, payload?: any) {
+    if (!this.events.has(name)) {
+      throw new OwlError(`EventBus: triggering unknown event '${name}'`);
+    }
+    super.trigger(name, payload);
+  }
+
+  dispatchEvent(event: Event): boolean {
+    if (!this.events.has(event.type)) {
+      throw new OwlError(`EventBus: dispatching unknown event '${event.type}'`);
+    }
+    return super.dispatchEvent(event);
+  }
+}
 
 export function whenReady(fn?: any): Promise<void> {
   return new Promise(function (resolve) {