[IMP] *: use a custom error class for all errors thrown by owl

This commit makes all errors thrown in owl use a custom error class. The
main point of this is to always wrap user-code errors that happen during
the owl lifecycle so that they can be treated uniformly in onError by
checking the cause property, and also allows user code to differenciate
owl errors from non-owl errors reliably at runtime.

tests/helpers.ts

@@ -19,6 +19,7 @@ import { helpers } from "../src/runtime/template_helpers";
 import { TemplateSet, globalTemplates } from "../src/runtime/template_set";
 import { BDom } from "../src/runtime/blockdom";
 import { compile } from "../src/compiler";
+import { OwlError } from "../src/runtime/error_handling";
 
 const mount = blockDom.mount;
 
@@ -221,7 +222,7 @@ export async function editInput(input: HTMLInputElement | HTMLTextAreaElement, v
 afterEach(() => {
   if (steps.length) {
     steps.splice(0);
-    throw new Error("Remaining steps! Should be checked by a .toBeLogged() assertion!");
+    throw new OwlError("Remaining steps! Should be checked by a .toBeLogged() assertion!");
   }
 });