[ADD] tools: create owl-devtools extension

This commit adds the code of the owl devtools extension.
This extension can be added on chrome or on firefox for
developpers to be able to inspect the contents of all owl
applications that are present on any web page, see all the
components, interract with them and their content to some
extend and perform a bit of profiling with their renders.

tools/devtools/src/devtools_app/devtools.js

@@ -0,0 +1,33 @@
+import { IS_FIREFOX } from "../utils";
+
+let created = false;
+let browserInstance = IS_FIREFOX ? browser : chrome;
+
+// Try to load the owl panel each 1000 ms in case it (re)appears on the page later on
+const checkInterval = setInterval(createPanelsIfOwl, 1000);
+
+createPanelsIfOwl();
+
+// Create the owl devtools panel if owl on the page is available at a sufficient version
+function createPanelsIfOwl() {
+  if (created) {
+    clearInterval(checkInterval);
+    return;
+  }
+  browserInstance.devtools.inspectedWindow.eval(
+    "window.__OWL_DEVTOOLS__?.Fiber !== undefined;",
+    async (hasOwl) => {
+      if (!hasOwl || created) {
+        return;
+      }
+      clearInterval(checkInterval);
+      created = true;
+      browserInstance.devtools.panels.create(
+        "Owl",
+        "../../assets/icon128.png",
+        IS_FIREFOX ? "devtools_panel.html" : "devtools_app/devtools_panel.html"
+      );
+      browserInstance.runtime.sendMessage({ type: "newDevtoolsPanel" });
+    }
+  );
+}