[IMP/FIX] playground: fix and improve various things

The playground hasn't been touched for a while and a few things were
broken before this commit:
- Exporting as a standalone web application was broken because it still
attempted to load the templates like it was done in owl 1
- Resizing the editor tabs still tried to use `this.trigger`

While fixing the export feature, the files needed by the app were
factored out of hardcoded strings and into real files, as this makes it
easier to maintain, since these files get syntax highlighting.

The samples received the same treatment: there is now a `samples` folder
containing all the samples, it also contains a jsconfig, giving
autocompletion on owl functions while editing the files, and allowing
the owl import to look how it would when using owl as a node_module.
In the browser, this import is translated to the relative path of the
owl module using an import map.

tools/playground/samples/responsive_app/responsive_app.css

@@ -0,0 +1,56 @@
+body {
+    margin: 0;
+}
+
+.app {
+    height: 100%;
+    flex-direction: column;
+}
+
+.app.desktop {
+    display: flex;
+}
+
+.navbar {
+    flex: 0 0 30px;
+    height: 30px;
+    background-color: cadetblue;
+    color: white;
+    line-height: 30px;
+}
+
+.controlpanel {
+    flex: 0 0 100px;
+    height: 100px;
+    background-color: #dddddd;
+    padding: 8px;
+}
+
+.content-wrapper {
+    flex: 1 1 auto;
+    position: relative;
+}
+
+.content {
+    display: flex;
+    position: absolute;
+    top: 0;
+    right: 0;
+    bottom: 0;
+    left: 0;
+}
+
+.formview {
+    overflow-y: auto;
+    flex: 1 1 60%;
+    min-height: 200px;
+    padding: 8px;
+}
+
+.chatter {
+    overflow-y: auto;
+    flex: 1 1 40%;
+    background-color: #eeeeee;
+    color: #333333;
+    padding: 8px;
+}

tools/playground/samples/responsive_app/responsive_app.js

@@ -0,0 +1,118 @@
+// In this example, we show how one can design an application that is responsive:
+// its UI is different in mobile mode or in desktop mode.
+//
+// The main idea is to have a "isMobile" key in the environment, then listen
+// to resize events and update the env if needed.  Then, the whole interface
+// will be updated, creating and destroying components as needed.
+//
+// To see this in action, try resizing the window.  The application will switch
+// to mobile mode whenever it has less than 768px.
+import { Component, useState, mount, reactive, useEnv } from "@odoo/owl";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+function debounce(func, wait, immediate) {
+  let timeout;
+  return function () {
+    const context = this;
+    const args = arguments;
+    function later() {
+      timeout = null;
+      if (!immediate) {
+        func.apply(context, args);
+      }
+    }
+    const callNow = immediate && !timeout;
+    clearTimeout(timeout);
+    timeout = setTimeout(later, wait);
+    if (callNow) {
+      func.apply(context, args);
+    }
+  };
+}
+
+//------------------------------------------------------------------------------
+// Responsive hook
+//------------------------------------------------------------------------------
+
+function createUI() {
+  const getIsMobile = () => window.innerWidth <= 768;
+
+  const ui = reactive({ isMobile: getIsMobile() });
+
+    const updateEnv = debounce(() => {
+      const isMobile = getIsMobile();
+        if (ui.isMobile !== isMobile) {
+            ui.isMobile = isMobile;
+        }
+    }, 15);
+    window.addEventListener("resize", updateEnv);
+    return ui;
+}
+
+function useUI() {
+  const env = useEnv();
+  return useState(env.ui);
+}
+
+
+//------------------------------------------------------------------------------
+// Components
+//------------------------------------------------------------------------------
+class Navbar extends Component {
+  static template = "Navbar";
+}
+
+class MobileSearchView extends Component {
+  static template = "MobileSearchView";
+}
+
+class ControlPanel extends Component {
+  static template = "ControlPanel";
+  static components = { MobileSearchView };
+  setup() {
+    this.ui = useUI();
+  }
+}
+
+class AdvancedComponent extends Component {
+  static template = "AdvancedComponent";
+}
+
+class FormView extends Component {
+  static template = "FormView";
+  static components = { AdvancedComponent };
+  setup() {
+    this.ui = useUI();
+  }
+}
+
+class Chatter extends Component {
+    static template = "Chatter";
+
+    setup() {
+        this.messages = Array.from(Array(100).keys());
+    }
+}
+
+class Root extends Component {
+  static template = "Root";
+  static components = { Navbar, ControlPanel, FormView, Chatter };
+
+  setup() {
+    this.ui = useUI();
+  }
+}
+
+
+
+//------------------------------------------------------------------------------
+// Application Startup
+//------------------------------------------------------------------------------
+const env = {
+  ui: createUI()
+};
+
+mount(Root, document.body, { templates: TEMPLATES, env, dev: true });

tools/playground/samples/responsive_app/responsive_app.xml

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+<templates>
+  <div t-name="Navbar" class="navbar">Navbar</div>
+
+  <div t-name="ControlPanel" class="controlpanel">
+    <h2>Control Panel</h2>
+    <MobileSearchView t-if="ui.isMobile" />
+  </div>
+
+  <div t-name="FormView" class="formview">
+    <h2>Form View</h2>
+    <AdvancedComponent t-if="!ui.isMobile" />
+  </div>
+
+  <div t-name="Chatter" class="chatter">
+    <h2>Chatter</h2>
+    <t t-foreach="messages" t-as="item" t-key="item"><div>Message <t t-esc="item"/></div></t>
+  </div>
+
+  <div t-name="MobileSearchView">Mobile searchview</div>
+
+  <div t-name="AdvancedComponent">
+    This component is only created in desktop mode.
+    <button>Button!</button>
+  </div>
+
+  <t t-name="maincontent">
+    <FormView />
+    <Chatter />
+  </t>
+  <div t-name="Root" class="app" t-att-class="{mobile: ui.isMobile, desktop: !ui.isMobile}">
+    <Navbar/>
+    <ControlPanel/>
+    <div class="content-wrapper" t-if="!ui.isMobile">
+      <div class="content">
+        <t t-call="maincontent"/>
+      </div>
+    </div>
+    <t t-else="">
+      <t t-call="maincontent"/>
+    </t>
+  </div>
+</templates>