fix: Bring back autofocus, sans the bug

web/src/app.js

@@ -25,6 +25,32 @@ const moduleName = body.dataset.appmapModule;
 if (moduleName in modules) {
   const div = document.createElement('div');
   div.id = 'app';
+
+  // Well, this is kind of gross. To make sure that focus is managed properly, we need to work around two bugs in the
+  // way VS Code handles focus for a webview.
+  //
+  // The first is that, after activating the tab with the webview, it sets the focus to the containing iframe, which is
+  // our `window`. We add a listener to watch for the focus shift. When it happens, we look for an element with the
+  // data attribute `focus`. If we find one, and it doesn't have focus, we focus it.
+  //
+  // The second bug is that, some time after VS Code sets the focus to the iframe, it resets it to the top-level iframe
+  // (the one our webview is embedded in). We don't have access to that window, so there's no way to add a listener to
+  // it. Instead, after a short delay, we check to see if the element we focused still has focus. If it doesn't, we set
+  // it again.
+  //
+  // As always, when you "fix" a problem with a delay, there's a chance that it will occasionally fail. But, this seems
+  // to work well enough to be worthwhile.
+  window.addEventListener('focus', () => {
+    const elt = body.querySelector('[focus]');
+    if (elt && document.activeElement === document.body) {
+      elt.focus();
+      setTimeout(() => {
+        if (document.hasFocus() && document.activeElement === document.body) {
+          elt.focus();
+        }
+      }, 200);
+    }
+  });
   body.appendChild(div);
   modules[moduleName]();
 }